After about two months in my new home, I re-installed new PEX hot water
pipes to all locations. I used 3/4" to the whirlpool tub, 3/8" all sinks
and lavatories, and 1/2" elsewhere. I measured flow rates before and after
and found no (or insignificant) decrease in maximum flow from the
sink/lavatory faucets but substantially reduced wait times for hot water in
every case. Since I made more home runs to the water heater, some wait
times were decreased because of shorter length of pipe. However, even
where the distance was the same, hot water arrives at the sinks lavatories
much faster than it did before because of the smaller volume of water in
the pipe.

I am not a plumber, but just from the physics of the flow I thought I would
be a good move and we are very happy with the result.