As a fellow home owner, not a pro installer/seller as the gentlemen above, let me throw this in for ya...
Soft water feels better in the shower, it's better for your (at least metal) pipes, boilers, and water heater. It allows soap to lather more. It is better for your hair and skin (possibly, depends on the individual).
It does not (IMHO) taste better, unless you have weird water issues. In my case, it was about 8-10 gpg of hardness with little to no iron. And it tastes much better hard than soft.
The way a softener works is by exchanging one ion of "hard stuff" (typically calcium/magnesium) for one ion of "soft stuff" (sodium). Therefore, the size of your system needs to be based on how many grains per gallon per day that you are trying to exchange. The softener will soften the water as long as there is sodium that is free to leave the resin and allow sodium to bind to the resin.
So if you buy too small of a system, you will need to regenerate more often to ensure water is soft. Say you but a 20,000K system, but with your usage and hardness, you require 20,000 grains per day to keep it soft... you will have to regenerate every day, and will be very inefficient. It seems conventional wisdom is to size a system to your hardness and water usage to regenerate about 7-8 days, but as Dittohead mentions, going 15 days is not an issue. If you use all the grains of sodium in the resin tank, then you will have increasingly hard water until you reach your raw hardness level (until you regenerate again).
Too large, and you can go longer, but you may be wasting sodium. Let's say you buy a 64K system, but only soften 2,000 grains worth of water per day. That means your resin will be able to go 32 minus one day (cuz you typically regenerate the next day at say 2 a.m. cuz you have to use bypassed water while it regenerates), so 31 days. Is that bad? Some will argue both ways. But for argument sake, let's say you decide to regenerate every 15 days... but you had 16 more days worth of sodium in your resin tank. Yet the cycle will use or bypass enough sodium to have regenerated the resin back to about 60,000 (my estimate, the experts can chime in as to the exact number, since any system will never regenerate nor handle as much as it is rated at). So all that brine is passed thru the resin, and flushed out into waste.
It's not like a 64K system will make your water twice as soft as a 32K system. Either system will soften your water until all the grains of sodium are exchanged for the "hard stuff". But a 64K system will require regeneration half as often as a 32K, typically. Whether or not that is EFFICIENT is what you need to decide, and size your system accordingly. There are also things to consider such as how many pounds of salt are being used per regen... 6 lbs, 8, 15.... this too plays into sizing a system. Based on the help from several here, I am buying a 7000SXT system rated at 48K that "should" be able to regen every 15 days to conquer 8gpg of hardness using 6 lbs of salt per regen, and use less than 4 bags of salt per year. Of course, this will vary with actual water usage.
Hope this helps simplify things a bit, it's what I have learned recently thanks to these forums. Great place to learn!
Sorry to say that you have a lot of that incorrect.
The exchange sites on the new fully regenerated (sodium form) resin beads attract the ions being removed based on their electrical charge, positive or negative.
Normally sodium chloride is used to remove those ions from the sites during regeneration of the resin. And 2 ions of sodium are released for each ion that is attracted to a site, not one.
Potassium chloride can be used to regenerate a water softener but, it is not as as efficient and you usually have to use more of it if you are using high efficiency salt settings. Plus it is very expensive if you can find it. There are no potassium form softening resins, all are sodium form. Kinda like using ethanol, it burns but doesn't produce anywhere near the power of gasoline, that the engine was designed to burn.
As to the K of capacity... Every softenr has an adjustable K of capacity. It is dictated by the cuft volume (and type) of resin in the softener and the lbs of salt used per regeneration.
A 48K (1.5 cuft of regular mesh resin) has an operational max K of 45K. To get that you need a salt dose of 15 lbs/cuft; 22.5 lbs total per regeneration. To figure salt efficiency you divide the 45,000 by 22.5; 2000 grains/lb used. If you used 9 lbs (6 lbs per cuft [1.5]) you get much higher efficiency out of the same softener.
Dittohead goes on about exchange tanks going a month between regenerations but doesn't mention the salt dose that resin is regenerated with so that can happen. He'd rather disagree with me.
New resin is fully regenerated when you get it in your new softener, If you use a high salt efficiency, you don't use all that capacity. What is left in the resin/softener is like when you buy fuel for your vehicles, you don't run them out before you buy more, you replace what you've used. You don't do that with resin either so, you leave the unused capacity in the softener. IF you ever overrun the K that you;ve regenerated you don't regenerate that capacity and eventually you will start getting hard water through the softener. Then you must regenerate all the resin sites and to do that you have to do 2 manual regenerations ate 15 lbs per cuft of regular mesh resin or all the sites won't be fully regenerated.
During regeneration the much smaller ions of sodium push the removed hardness and any iron and manganese ions off the site leaving 2 sodium ions in their place. When the softener goes back into Service, those 2 ions are pushed off the site by hardness etc. ions and into the water stream.
Six lbs of salt per cuft of regular mesh resin gets a salt efficiency of 3333 grains per lb; or 20K/cuft, a 1.5 cuft softener, called a 45 or 48K, gets 30K with only 9 lbs of salt. The remaining capacity 45-30=15K is still there. Just like the remaining 1/4 tank of gas when you refill your fuel tank each week etc.. And your right foot controls your fuel efficiency. Zipping from one red light to the next and stopping instead of slowly getting to the next light as it turns green and you fill up more frequently while wearing out your brakes etc..
Exceed the gpm flow rate of the cuft volume of resin in your softener and each time do that you use up some of that 15K mentioned above. Do that frequently and your softener won't be doing much softening until you fully regenerate it twice at 15 lbs/cuft to fully regenerate all the resin sites. That gpm flow rate is the most critical part of correctly sizing a softener but, sad to say, most sales people never mention it.
Things in water give the water a good or bad taste. Good water has no taste. It is said that it takes 21 days to make or break a habit. We like what we grow up with or are familiar with, especially when it comes to the taste of water.