Very confused about shower connections

In a previous thread I questioned the size of the supply lines required for a shower renovation I'm planning.

I was told to use 3/4" vs 1/2" for all connectins.

Looking at the different parts the manufacture supplied with the system.
I've noticed the connections on the values are 3/4" but the connections on the body sprays, shower head and hand held are all 1/2".

I've been told the 1/2' will not supply the amount of water needed for the system I've purchase.
Why would a manufacturer(moen) make the connections 3/4" at the values and reduce to 1/2" at the fixtures?
Doesn't this cause me the same potential problem as going from a 3/4" main run down to 1/2" supply lines?
I don't see the difference between reducing on the input side of the value VS reducing on the output side of the value.

The valve supplies many heads and my use a 3/4" loop, of which it may supply several heads off of that.

Individual heads only need to be 1/2"

If you are so determined to run them 1/2 go right ahead. You'll figure it out later.