I don't think this is a question of playing hands which you wouldn't otherwise play. You might want to say that you think a hand is marginal when you post it, but you are playing it because you believe it is correct to do so.

I think there is a set of hands which we all play almost all the time - things like pairs of aces or kings, rolled hands, big live flush draws etc, which have a high positive expectation. Up to and including 5/10 (and possibly higher than that) it's pretty easy to be a winning player just playing these hands. I suspect that this is a strategy used by a number of posters here, and it is an effective and relatively low variance way of making money in these online games.

I think that there are a number of other hands, which are (or can be, if played well) marginally profitable. There is a section in 7CSFAP about playing some pretty junky hands in late position in unraised pots. As well as playing these hands for the potential profit, I think that it is correct to play for meta-game reasons, but also to improve your skill and judgement. Indeed for those reason it is correct to play hands with no positive or negative expectation.

A couple of examples - when I started posting here, I asked a few questions about whether I should play hands like A44 against a raise or reraise from cards like queens and kings. Most people here suggested that I probably shouldn't, although nobody demonstrated that I would actually lose money doing so. Another example is that a number of people are unwilling generally to call a small bet on fourth with a gutshot. People also suggest folding a flush draw on third, if there are two cards out, even with a fully live overcard to the board. I think that these are all situations that should be played unless there is a good reason not to.