Pumping milk before baby is born? Opinions.

I heard some woman say they pumped milk before baby was born well not so much milk but the Rich "milk" forget what it's called. I think I want to just so I have extra for her to eat. But at the same time I wonder if any other mommy's out there have done this? I always am leaking "milk" so I might just start pumping once a day for a little bit to relive some of the pressure and pain and save it for her. If I do this can I add the new "pumped milk to the old pumped milk if it was from the day before? I'm just wondering. Like if I froze the milk the day before pumped again and added it to the frozen milk than threw it back in the freezer would that be okay? Any other mommy's do this? Opinions?