From a purely economical standpoint, you might as well just send the excess.
If you played zerg I could understand sending more for defensive purposes vs T for example. Plus it's a bit trickier because you don't necessarily produce workers at the same rate per hatch. So you could potentially end up worse off, it's not clear to me off the top of my head.
But for P/T, I can't see a reason to split evenly. This is actually good cause I was wondering about this a long time ago and I had been meaning to sit down and think about it.
Terran is fun just because there are so many ways you can play it
Yes having lots of builds is very nice, I feel like I pretty much dictate the action rather than having to react. Its nice to beat people that Im better than instead of going 50/50 too. Pretty much all my OP suspicions about T are being confirmed.
Terran is just a silly race with all kinds of small OP advantages. Like today I went 6 rax mass marine in a team game, ended up losing all of my SCVs to a huge ling run-by, and yet I was still able to keep a reasonable number of marines pumping with just MULEs.
Yes theres so many small things. One things that huge for me is being able to build your CC somewhere safe before you expo so much easier to macro safely where as any time you expand as toss its a huge liability.