If you have a build that has effects that require critting or vuln.
It’s now in competition with other additive damage though, unless there’s a paragon node or something that scales with the stats. Like maybe Barb will have something where you get 10% of crit damage as attack speed, so it will be worth stacking crit damage over other additive mods.
Depends on how much damage you could get in other ways with those same things you’ve invested in crit chance. Might not end up being worth it if you have to choose between crit chance and some other stat that turns into a x% mod.