Is it an essential mod? I dunno... I think maybe for some applications, like a Panerai... Perhaps. Even in moderately lit rooms, the luminous can be quite visible on gens, especially if you've just come inside from a sunny afternoon.
For other models, like IWC and the sort, it's probably a lesser priority as the luminous material they use isn't very strong.
If you like vintage watches, it's a non-issue since most tritium dials and hands have already gone dim due to most applications approaching or passing the tritium's half life.
And... Some people just like to have it for sake of having it done. Since super luminova doesn't deteriorate over time, it's a long lasting mod. Or, in the case of the gen Omega dial in my first post, it's a nifty bonus when you add such a dial into a rep case