Unless your amp has an "idle" feature, leave it on all the time. For the rear channels of my system, I use an old Marantz PM94 integrated amp, which is left on all the time. Everyone who I've ever spoken to who owns one of these things has found that they blow up after a period of time--the result of heat cycling. Not my PM94. It's been working continuously for nearly 8 years. Heat cycling is bad news for solid-state equipment.
