Well yes, I think warnings and tags and stuf is a good idea, specially because sometimes it is pretty usefull.

I say sometimes because most of the time I just don't read the warnings, I welcome every surprise, however sometimes I don't feel like facing certain kind of stuff, and a warning is always a nice way to avoid it.

No, I don't think there's such a thing as a silly or useless warning or tag, I just think that sometimes it is kinda hard to say that a something, let's say a fic, can be related to a certain tag, but that's just sometimes.