If they are sugar cookies, refrigeration is required so they don't lose their shape because they may spread out in the oven. If you don't have time to refrigerate, just put them in the freezer for as long as possible, then bake.
Refrigerated cookie dough often has a better flavour.Â Other main reason is being able to handle dough... easier to cut and shape chilled dough.
It may be a pain to roll out and may spread in the oven.Â Other than that it will be fine.Â If you can handle the dough, refrigerating or even freezing the already-cut-out cookies will be very fast and then you can bake them.
Let the dough chill at least 4 hours. Â The cookies will have a very different texture if you bake immediately after mixing.
They just seem to taste better when the dough is refrigerated overnight. Also, I always put my cut dough in the freezer on the cookie sheet for about 15 min. before baking to reduce spreading.