I'd never used it for my Tmax400 in Xtol, nor my Rollei Retro 100 & APX100 in Rodinal (those are the main 3 that I've dev'd at home lately), although I'd read on the Tmax datasheet something about needing HypoClear or it goes pink. It never went pink.
Then I did a roll of Tmax400 and my first roll of TriX 400 together in the same tank in xtol. Fixed in Ilford RapidFixer as I always do, washed using the Ilford 5-10-20 washing method, hung them out to dry, and the Tri-X was pink. Very pink.
So the next day I went and got some Kodak HypoClear, didn't want to mix the whole 5L so I just put one spoon in one litre, re-spooled the TriX and washed it again, it turned out fine.
It's one of those things that, if you don't do it, there's a chance something may go wrong, but there's no downsides to doing it besides spending a bit of cash. So I'm probably just going to do it from now on (at least for my TriX).