It's a worry when people boil down human communication to pure information theory. This interwebs commenting platform is a human experience, and you're sharing and creating an experience for many others with your words; this does not appear to be covered as a consideration in your 3 categories.
- Asking questions
- Answering questions
- Education (I put debates in this category, since frequently I'm the one learning)
The nice things about these is that votes form a good indicator as to how well I wrote my point of view. It's not a perfect metric since downvotes punish divergence from the community consensus as much as they do poor content, but it's generally good enough.
And by attempting to limit myself to those categories, my time is not wasted. I do accept that I'm going to fail from time to time by posting pure fluff, and that's OK too: at a bare minimum I've put some practice into my writing and social skills.