How much data to save

[John Doe]

Greetings,

After taking an general course on databases I decided to start over with a relatively large project of mine. I need to manage a number of users, groups, and services, and I wonder how much information is feasible to store. For example, would storing information on every single request by a user to be accepted into a group and who accepted or rejected each request be a smart move? Would the benefit of providing users with additional historical information outweigh the small increase in storage requirements, or should I preserve minimal storage whenever I can?
I understand this is a very domain- and project-specific issue, but I hope some of you might be able to give me some general hints.

Best regards