The only problem is it has to be done right. Say you use a newer printer and it's compromised.... you could lose it through there. Rare yes but not impossible. The dumber the printer the better, also if you print a wallet might look into how to clear cache on your printer.
Power it off?
I dont know about you guys but I have a normal printer that prints only. Not with wireless crap and other stuff that has attack vector.
I just power off the printer, and the cache clears, because it doesnt have memory card and things like that.
-snip-
This is mainly for commercially used printers. In which case a power off would not help either, because they use a harddisk for long term storage. AFAIK this is not common on end user printers.