Bats fly at night, so if their access to roost is sealed up in the daytime, they will be sealed in. I'd rather seal the area up at night and give them a chance to find someplace else to roost. Having bats around is great bug control but I sure don't want them in my house! So far, so good although there always seems to be a couple who persist in trying to live in our workshop attic. That's our storage area, so we don't want bat droppings all over everything. Ick.