It's not a bad idea to take 3/4 to the last "T" in the system , then
take the last two branchs on in 1/2" . BUT do keep in mind, that on
the hot side, you'll be slowing down the hot getting to the fixture.
You might have to call the public services department in
your town, and get 3/4 inch water instead.
More seriously, it will make little difference, except....
if there is a long run of pipe, or lots of elbows and shut
offs, the 3/4 has lower resistance to flow. And it will take
longer for the hot water to arrive.
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