Totally agree with Mid and RJM... Bigger and slower means less options as a position player, which means less potential opportunity to crack the lineup and more limitations presented to your coach. And clogging the bases is a definite component in the equation.
I was playing around with lineup options last night for our HS program. I kept feeling compelled to slide down two of our most potent hitters (and create space between them), largely because they are strong GIDP candidates in spots behind guys that will get on base a lot and this will likely kill lots of rallies. Yes, of course, if they are potent bats, they will also often drive those runners in (which is obviously the goal) but the DP likelihood definitely factors in. If they have at least "somewhat acceptable" footspeed, that helps.