Jake Brake on/off switch....

[Kranky]

The only thing you have to really watch is that you aren't using your clutch to keep the jake from engaging by resting your foot on it.

Rev,
Last year I was told by my trainer to keep my foot on the clutch lightly so that it would not activate in a city or part of highway forbidding engine retarder use. Reason being that if I needed it then I have it ready. The other reason was when I would get through the location I might forget to flip back on and find out as I began going down a grade.
I always thought that leaving the clutch partially engaged wore on the clutch, but was told nope.
Is this the reason you say not to rest your foot?

Although your question was not addressed to me, I will say that resting your foot on the clutch pedal for any reason will cause unnecessary wear to the clutch throwout bearing, and beyond that, resting your foot on the clutch pedal with a little too much pressure will cause clutch slippage.

Clutch slippage leads to a ruined clutch, which leads to a premature clutch replacement.