"Evil" can really mean anything from extreme wrong to innate desire to oppose "good", its colloquial use is very free-flowing, so there is a lot to be confused about by it linguistically (or else I'm just easily confused). Supposedly its original meaning was closer to what we'd associate with "cruel" or "harmful," which is nicely enough more concrete. To me, though, even if you're using it in one of the less dramatic contemporary senses to mean something extraordinarily immoral, in order for the meaning to have much reach I would still need to be convinced of the existence of a more or less objective moral system, which is a whole discussion in and of itself. Maybe if it were taken to mean something like "innate desire to cause pain or behave cruelly" I could see it having traction. I don't think it's usually used that way, though.

I mainly avoid it in speaking and thinking because I find that it has the net result of dehumanizing very human flaws and misdeeds. I also think that that's part of the concept's appeal when you get right down to it. Using it often allows us to put distance between our idea of ourself and the nasty things a meaningful class we belong to (person) is capable of. The word and its various definitions/uses are more a vehicle for that distancing than any one fixed thing most of the time, from what I see, so unless distancing is part of the goal of the discussion I think its usefulness is usually limited, provable in some way or not. In a way I think the idea of it tends to trivialize tragedies more, by implicitly trivializing our relationship(s) to them and their frequent causes.