Bats are overall good for nature, and are also protected by law. Each one will eat thousands of bugs a night.
Having said that, bats only need an opening of about 1/2" to get into your home. They'll roughly double in numbers every year, and are hard to get rid of if you don't know all of their entrances. The guano, let untreated, can cause structural decay and mold growth.
At McGinnis Wildlife Control we're equipped to get rid of your bats, and do the necessary cleanup and restoration. Give us a call to schedule your consultation.