<p>I'm new to 3D printing and I was wondering about the risks of leaving my printer to print overnight? I'm aware that if something goes wrong I'll wake up to spaghetti for breakfast but what are the other things like having the nozzle and bed heated that long? And, when it's done it just sits there on so what could that do to the screen? What if the printer runs into some physical problem and damages itself and/or the print? I'm not looking for answers to these questions specifically just feedback on what I should do when printing overnight.</p>

Presuming that you're talking about an 8 hour period, your printer should be designed to run for 8 hours continuous anyway, so nothing will happen regarding the bed or screen that wouldn't happen with a normal print.
If the first few layers stick to the bed, it's likely that you're print will at least be partially completed. So even over night it won't be a full 8 hours of printing while failed. Maybe half that period.
If the problem is bed adhesion, or anything that doesn't effect the filament being supplied to the nozzle, then your only problem will be wasted filament and disposing of the spaghetti. No harm will come to your printer.
If the problem is a break in the filament or filament runout, or a blocked nozzle then you could have damage to the head of the nozzle from printing dry. If you're printing with PLA this isn't really something that you need to worry about too much as you can run a printer dry for several hours without any problems.
If you're printing with ABS or something that needs a hotter head then you could cause damage to it if it's allowed to run dry for an entire night. But again this isn't really something that you need to worry about unless it's running dry for 4 or 6 hours.
Simply checking in on it once in the night should be enough to prevent any problems.