All I've heard is from one lady who said it brought her intense labor pains, worse than her first two kids. Granted, she pumped for over an hour in one sitting.
Well what you might be pumping is the "pre-milk" which I can't think of the name for it right now.
And the baby really only drinks that until your milk supply comes in, hours/days after birth. I don't think your actual breast milk will come from pumping? So I don't know if there's an actual point to it (you might have to Google that)
Nipple stimulation has been known to bring in contractions, and causing labor in the long run.
Just do whatever you want to do.
Nursing while pregnant is usually fine if you are not high risk. Pumping can start labor.
Nursing during pregnancy is fine if you were already doing it prior to your pregnancy. Collostrum is what leaks during pregnancy and that sticks until about 2-3 days after the baby is born when your actual milk comes in, no need to stash because babies only need so much colostrum! Also, pumping and nipple stimulation when your body isn't accustomed can start labor because it releases oxytocin which is the hormone that is released to put you into labor!