When things are built...to pass the plumbing test(s), the connections must be leak free. Then, the walls/ceilings are closed in. Things don't magically leak in the wall/ceiling after time. Cartridges, seals, etc. can and do leak. Most can be fixed from the finished side. A toilet won't magically start leaking if it is installed properly.
Having an access panel to fix something that shouldn't need fixing, if it works for you, fine, but is not that useful. IF there's an adacent wall where you can actually put an access panel, then, there's no reason to put one there until, and if, you need to do maintenance there that can't be done from the finished side.
Now, certain things really should have an access panel...these include things that are known to wear out and not commonly triggering a major remodel. For example, the motor of a whirlpool tub. While it should and does generally last a long time, it may need maintenance before the tub wears out too, so would qualify for a good reason to have an access panel.
Sprinkling them around the house, especially if they end up in visible areas, is not very common or useful.
Go for it if it makes you feel comfortable, but it is generally a waste of time and money and asthetics.