Setting up UBL for the first time on Marlin 2.x on a Prusa i3, how often should I level the bed using G29? I used to use the Marlin 1.x software that would level the bed by probing the 4 corners of my print bed (a long time ago, it's been at least 2 years since I used my printer, wasn't able to set it up after I moved).

My slicer had G-code that would kick off a level at the beginning of every print.

I've upgraded to Marlin 2.x and now I'm setting up UBL. It takes quite a bit of time to probe the bed with UBL, like 10 minutes. The steps tell me to save to EEPROM and my firmware is set up to restore after every G28 (Home).

How often should I do a G29 (Bed Leveling)? Should I do it every print? Every 10 prints? 100 Prints? Or when I see that the print isn't sticking to the bed?

EDIT: I went from a Grid-style ABL to UBL because UBL merges the benefits of a few different leveling techniques so theoretically it should be better. I understand I could just go back to grid-style bed leveling but even when it was working, for some reason the z-offset would shift ever so slightly every few prints and I would have to change configure it in my slicer. I'd like to try UBL and see if I can leave my printer for a while without having to fidget with the Z-offset.
This is more of a personal preference type question rather than something with a hard and fast rule. 

You should not need to relevel your bed very often unless you have some external force that regularly changes the bed level.

I regularly print objects that take 24+ hours to print, so a 10 minute process prior is not much so it might be worth it to set it up every time if your prints run very long. If you mostly print smaller or quicker to print objects, 10 minutes might matter to you.

I have noticed that my prints fail pretty quickly if I have a leveling issue, and it's not hard to stop the print, clean the plate and relevel at that time.

What should you do?

If 10 minutes doesn't matter that much, go ahead and relevel with every print. If it matters, wait until you start to have issues. See how long it takes for your bed to become unleveled and use that as a guide. E.g. if you can print 10 times before having issues, then try setting it for every 6 or 7 prints.