Honest1, For most applications where both low and high pass filters of the plate amp are used, the plate amp does ease the load of your main amps.
In my case, you are correct, though by using plate amps on the subs, I don't need to use as much of the MA-1's power to get to my desired spl level. Also in my case, my sats present an easy 6 Ohm load with 90db sensitivity and the MA-1's, at 140 wpc, are overkill. Actually, I've driven them with a friend's Coincident 8 watt 300b Frankensteins to great effect.