Its a lot more secure when the top of the case at a minimum is aluminum. For some that are running Higher end radios and such that want the most out of their Car, it is the easiest way to avoid any discrepancies in the servo. Also the fact with the newer Servos and HV the case can act as a heat sink to dissipate heat better.Not to mention the are a bit more robust as well. I run full Alloy cased servos in 1:8 Truggy and 1:8 Buggy.