Weather can change at any moment, so when you are camping, you want to make sure your tent is sufficient. After waking up one morning trip as a kid in a puddle and not being properly dry for a couple days, I always waterproof the seams. It is surprisingly easy to waterproof a tent.
First thing, put up the tent and make sure it is dry and clean. If there is a glossy appearance on the seams of the tent, that means that is it already coated with waterproof solution. To new tents, apply the waterproof solution to the opposite side of the original coating. If the tent is old, apply to both sides. As it is drying, apply a second layer and remember that is can take a while for the waterproof solution to dry. It may take as long as a few days so make sure it is dry before taking the tent down.