Infiltrators are also excellent defensive units. When backed up by anything capable of quickly destroying Maulers. As an example, on the Endor Xpress map against 3 human opponents, I was able to hold them back (this was 3 against 1) almost indefinately using only infiltrators.
By the end of the round I had destroyed 6 AT AT's, about 60 AT AA's (they were being used as an assault unit), and countless AT ST's. Fortunately, very few maulers were sent.