Thing is, most arrangers don't have an independent volume control for the headphone outputs, so if you want to send a decently beefy signal from the main outs, the headphone outs are going to be pretty much up there (compared to line level). This is where, if you have a need for using the headphone outs AND the mains, one of those little attenuators is a handy dandy piece of kit to have in your cable case. Many boards (I know the big Bose's don't have an RCA attenuation knob, didn't know the Compact has it - about time, too!) have little control over the RCA outs and ins if any.

One of these can save your butt when all else fails. $10 well spent...

PS, I've also used these to attenuate RCA outs going to digital recorders that sometimes (H2, for instance) have no analog input attenuation. 1001 uses!