The Tesla Tower is the 2nd of the high-ranged (without the Railgun) defensive towers. The first one is the Sniper Tower, the 2nd is the Tesla Tower, and the 3rd is the Cannon Tower. Tesla Towers can attack both aerial and ground monsters. The Tesla Tower is capable of taking out D.A.V.E.s (without a Zafreeti). A good strategy would be to put your Tesla Tower near your Town Hall, as a high level Tesla Tower has a very high range and damage. However, if the attacking monsters are healed by Zafreeti, the Tesla Tower is useless, as the Zafreeti could heal the monsters completely between shots.
The tesla tower has a huge amount of reload time, just like the quake tower and railgun. So you must protect it with powerful buildings, otherwise it might get overwhelmed.
Also, lagging can slow them down to the point where they fire extremely slowly and cause minimal damage to the monsters.
The Tesla Tower is much more effective if it has been fortified completely.
The Tesla Tower at lvl 8 has a lot of damage (8400 damage per round) and could easily take down a small group of D.A.V.E. quickly (especially if the D.A.V.E. isnt fully upgraded) if it is highly protected so if dealing with a yard with high leveled teslas it is recommended to catupult 1 or 2 and aim your monsters towards them.
When designing your yard it is recommended that you spread your teslas out but still be able the cover almost your whole yard, especially your town hall.