6 years ago I started riding on the road. I didn't know anyone else local who wanted to do that, and I didn't have much fun by myself. I joined a road club, and spent 2 happy years busting a gut every Sunday morning to make sure I was at the appointed place at the appointed hour for a long, sociable and varied ride with some splendidly skilled and encouraging riders, several of whom I was entirely happy to have a beer with (others one simply chatted gently along with on the ride).
3 years ago I turned up in a new city by myself. I knew a few people slightly from the internets and from very casual acquaintance at races. My mountain biking has mostly been done through very welcoming networks of mates which borderline qualify as clubs. My road riding has been with a club, which is an enormous reservoir of enthusiasm and goodwill, and promotes a major road race that would otherwise probably not happen.
An extended network of mates on the internet is a relatively hard thing to break into. A club says "we meet at this time, please come with us" - a standing invitation to all comers to join a ride is a very welcome thing if you're in a new place by yourself, or trying a new thing by yourself.