Today's electronics are deigned to be safe and economical to operate.  However, leaving devices on 24/7 does eat a substantial amount of electricity, regardless of the device.

Power adaptors are notorious for using more power than the device itself.  This is especially true of cell phones, for example.

It comes down to how much you're going to be printing. Most people usually use their computers off and on all day, so they leave them on all day and then just turn them off at night to save some power and also for safety reasons.  All-in-One printers may also be used as a fax, so they need to stay on all the time regardless

If you're going to be printing off and on all day long, you might as well just keep the printer on until you're completely finished. If you're just going to print one item now and then, and then not print for a few hours, turn it off.   Most printers turn on very rapidly, without long warm up cycles.

The main two reasons to turn your print off are: electricity usage and ink cartridge print heads drying out. The bigger of the two issues may be the drying of the print heads, because inkjet printers really don't use that much electricity. The newer ones use even less, but older printers (unless a laser printer) don't really use that much either.

Most ink cartridges have some sort of a capping mechanism that saves the head from any outside air that may come through when the printer is turned off. But, if you leave the printer turned on all the time when not using it, you're just asking for your cartridges to dry out, and will have to buy another cartridge that much sooner than normally would be the case. If your print heads dry up or clog, your printing quality will suffer also.

Therefore, always make sure you turn your printer off when not using it.  But remember to turn off your printer by the On/Off button, and not by flipping your power strip or UPS. When you use the printer's own On/Off switch, the printer will engage its capping mechanism to prevent cartridge dry-out. Otherwise, it will freeze in whatever state it was in, and your cartridge will still be at risk for drying out.