From what I understand, towers chaining together is basically just increasing the range of a tower. Say a towers range is 8m... you are in range of a tower 5m away from you but there is a second 10m away from you that is too far away. The tower that is 5m away will shoot at you, then the tower 10m away whille shoot at the 5m tower, and the shot will "chain" through that tower to hit you. So you'll be hit with two shots from two towers for normal damage.
I hope that made sense. .. I actually use this to my advantage quite a bit with the tower build. I'll often make a line of towers connected to the normal towers that the map starts with, and have one all-powerful tower at the front of it that's firing out multiple shots for all the other towers.