grow because you want a big pumpkin but also because you are tired of burying vines and you want the pumpkin to take off so the vines will slow down. around day 28 typically the pumpkin has gotten big enough that it has become a sink and most of the energy in the plant starts flowing to that sink. at that time you will see the vines, which have been growing 8-12 inches a day, slow down to 3-4 inches a day. life is easier when you can watch the pumpkin grow rather than bent over covering vines.
however, having said that, burying vines right now is probably the most important 