Decrease investment risk (invest in more startups); decrease deal costs (e.g. due diligence, legal fees, organize meetings/pitches).
The management team of the club is focused on generating deal leads; Every member is also responsible for referring deals.
There are really crazy ideas/founders out there that can waste huge amount of your time and energy.
Keeping low profile/anonymity if you want.
Improved deal terms as a result of investing collectively
Learn from each other, do business & have fun together.