What are the potential risks of joining a Steam group?

Does joining a Steam group give that group any additional information about you? Does joining a Steam group open you up to potential fraud in some way?

The source for this question is to understand the rational behind people spamming group invites.

If two people are in the same group, they can message each other without being Steam-friends. This is a potential scam/spam vector. However, it's not a common one, in my experience.

I think the actual reason for the excess of group-invites on Steam is the same as the reason people spam guild/clan/server invites in many games, despite a large number of people conferring no advantage: they just want their group/server to be more popular. I've found this is especially true among younger gamers, because it allows them to be "the boss," a role they don't typically get to play in the real-world.

So my advice is to join as many groups as you want, but only the join the ones you actually want to join. They are unlikely to do you harm, and you can always leave them later.

Additionally, groups can set events which will cause windows to pop up on your screen alerting you of the event. These won't go away until you close the windows. This is potentially annoying and can't be disabled.

You can be messaged by another member of the same group without having them as friend.

They will also be able to join any friends-only sessions you might have running at that moment, such as Friends-Only lobbies in PAYDAY 2, or a friends-only game in Borderlands. But the chances of that happening are pretty slim (even more so in large groups), and you could always just kick them if it happens.