I just started to review posts in Stack Overflow. By this page, I know why flagging is important. But:
- Does it have any impact on my reputation?
- What is the impact on my profile if I have a lot of helpful or declined flag?
All it really achieves is help keeping the site clean, friendly, useful, etc. In the event of a moderator election and you nominating yourself it might be useful to have a good flag count and helpful percentage. But that's about it.
It's more about helping to keep the site be something you want to come back to, rather than directly doing something for your own profile.