One way an amp can damage a speaker is by supplying DC current, either by internal damage or a faulty soft-start circuit (the "thud" you hear when powering up). This, if it happens, is independent of downstream source components. If your amp is okay, I agree, you can safely power it up with no source components.
I don't think you need to be reminded to change connections only while every component is unplugged. Don't place faith in the power switch alone.
I don't think you need to be reminded to change connections only while every component is unplugged. Don't place faith in the power switch alone.