It basically 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 throughout the day and then just turn them off at night to save some power and also for safety reasons. So, you can use the same rules for your printer. 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 and then not print again for a few hours, turn it off!
The two reasons that go around this are electricity usage and ink cartridge print heads drying out. The bigger issue here may be the drying of the print heads, because printers really don't use that much electricity. The newer ones use even less, but older printers 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. If you leave your printer turned on all day when you're not using it, you're just setting yourself up to have to buy another cartridge much sooner than you normally would. If your print heads dry up, your printing quality will be poor as well.
Make sure you always turn your printer off by the On/Off button and not by flipping your power strip device. When you use the On/Off button, the capping mechanism I mentioned above will fully engage and do its job correctly. Otherwise, it won't and your cartridge will still be at risk for drying out much too quickly. Here's to keeping your printer the best it can be!
