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It just depends on the person in my opinion. We can't say it's generally good or bad, because different people experience different things from it.
I've been in two official online relationships so far. First in 2006 and the other one 2 years ago. Neither of them worked out in the end, but I don't regret dating the girls. In fact, I'm still friends with my last ex.
I've also been in this situation with an online friend at the moment. Right now, things are pretty tough even though our feelings are mutual. But if nothing else blossoms from it, she'll always be my friend and I'll always love her. So it essentially also depends on how you perceive the whole thing, too.
There's Peter Pan in each of us.