The existing supply lines are 1/2".

The thermostatic control shower valve has 3/4" ports.

There are 2 volume control valves - one for a standard wall shower and one for a handheld shower. Each volume control valve has 3/4" ports.

I was thinking of running 3/4" the feeds to the volume controls and the related showers from the thermostatic control instead of 1/2". The thinking behind this is to capitalize on the full 1/2" volume of each the hot and cold feeds.

Is this going to somehow throw off the effectiveness of the thermostatic control valve? Create other problems? Never seen a plumber do this before but maybe it's because the materials cost more and they'd have to bring in 2 sizes of pipe instead of one. They're keeping it simple.