Why? Studies show a single bat may eat as many as 5,000 mosquitoes in one night.
Some tips:
1. Your bat house should be situated to receive maximum solar radiation, especially in the morning. It should face east to absorb the morning sun yet be shaded from the blazing heat of the afternoon.
2. Mount the house at least 10 feet high under the eaves of a house or garage or in a tree sheltered from the elements.
3. If your bat house is not occupied by the second year, try a different location, or place more than one house initially.
4. If you live near a pond, lake or river, your chances of success are increased because bats need a source of water for drinking purposes. However, don’t be discouraged if the conditions are not perfect.
Do It And How 
Just a word of warning. If you hang a bat house like that on your house you will get poo streaks down the side of your house. Best to hang it where the kids aren’t going to step in the waste, and it doesn’t end up down the side of your house.
We have a lot of tall trees at the edge of our yard/property, that’s where we’ll hang ours. Thanks for the info!