For units that can already crit with their ability, when is it acceptable to build IE or JG on them?

Had this question for a while. I heard from streamers before that a big part of Infinity Edge and Jeweled Gauntlets's power is the ability crit, and if your unit's ability can already crit or if you have something like Jeweled Lotus, you would prefer to build other items if you can.

For example, streamers this set say not to build IE on Draven, since his ability is just autos and those can already crit, so a lot of IE's power is wasted.

But for some (not all) Ambusher and Executioner units, it seems like IE and JG can be good items on them even though the trait already gives these units ability crit.

For example, IE is BIS on Jinx this set, and from what I've seen, Urgot and Vex in Set 14 also use IE/JG really well. But at the same time, IE isn't BIS on Smeech and Camille and JG isn't BIS on Ekko (even though they can use it).

How do you tell when IE/JG is good on a unit that can already ability crit? Is there some way to tell from reading the ability or is it mostly just wait and look at the stats?

I know you can't always get BIS so slamming is fine but would love to know the reasoning behind why its sometimes good (and bad).