Turning any gear (with the exception of class A amps which draw considerable power in standby) off and on repeatedly is not a good idea. IMO, the stress on the components (the downside) is greater than the upside. I turn my amps off and on every night, and leave everything else powered up all the time.
Unless the bias is set too high, and there is a pinging sound coming from the speakers, there is no reason to worry about the membrane.
