I think back to how I used to wax quite frequently and I simply

about it. And yeah, QDing after every wash can really help LSPs hang on....sacrificial layer and all that.
The frequency for me really depends on the LSP; I'm using four different ones at present (won't count the Jag as it's still in mothballs but it gets Souveran at every wash).
UPP gets redone quite often, but it's only on the garage-queen S8 so the frequency isn't representative of anyhing IMO (e.g., drive it four-six times/year, UPP it twice). But the point is that UPP simply doesn't stay slick IME, nor does it protect so I'm really just using the stuff up.
476S gets redone about twice a year, but it's on the limited-use '93 Audi so that doesn't really track either. On a daily driver I refreshed it every three-four months.
M16 on a daily driver gets redone every other month or so to keep it in "just waxed" condition, but I can sometimes stretch that another month.
The FK1000P x 2-3 seldom needs redone *annually* even on daily drivers. It lasts even better for me than KSG X 6 did, by a pretty wide margin. Simply incredible how the stuff lasts for me (and how it apparently does *not* last that well for others).
In all these cases I redo as soon as that "just waxed" effect starts to diminish, long before the beading goes flat or the surface loses its slickness to a significant extent. I honestly can't remember the last time one of our vehicles seemed like it really *needed* waxing.