Most of my relationships have been online ones. Most of the online relationships weren't planned, and sorta just happened.
It's hard being unable to do normal relationship activities like going to see a movie or have sex. Video calling helps with the distance a bit.
It seems to me that women have a larger problem with the distance than men do, at least it is in my case. I do miss my spouse when I'm in an online relationship, but the distance always seems rather unbearable for my spouse.
While I think in-person relationships are far better, a benefit of meeting someone online is that it removes the physical attractiveness factor in terms of wanting to get to know a person better. A good personality always triumphs good looks. Normally when you meet someone, tiny little things about their looks can quickly influence whether you want to get to know that person more or not. When you've already established a connection with that person, finding out what they look like and seeing they have a little inconspicuous mole or birthmark on their neck doesn't influence you at all really. Sure, if they turn out to be really unattractive, that is going to influence whether or not you want to continue that relationship.