Playing MTTs with money added ( ____ guaranteed)

[Asgrow13]

So I'm extremely new to mtts, but I noticed that a lot of them say ______ guaranteed meaning if a certain amount of people don't enter, the site will add money to the prize pool. Do a lot of these tournaments end up actually running with a substantial amount of extra prize money thrown in by the site? If so, that seems like it would make them extremely profitable for a mildly decent player. Am I missing something here, or is it a common strategy for MTTers to seek out these tournaments? I'm mainly looking at the $24+2 and $69+6 type events on full tilt.