I'm just gonna go out on a limb and say that leaving them plugged-in indefinitely is not good for them.

I am not an expert but with limited knowledge, power going into your devices isnt uniform depending on what's being used in your home.

So these ebbs and flows of current into your devices will wear out the electrical components over time.

I'd say unless you play retro games regularly, keep the consoles unplugged until you decide to pop a cartridge in.