> Why the count is important?

If I am not mistaken the flag allowance (how much you can flag in a day) is tied to that stat.

> Does it lead to a badge or some reputation up?

There are two badges for 80 ([Deputy][1]) and 500 ([Marshal][2]) helpful flags.


  [1]: https://wordpress.stackexchange.com/help/badges/67/deputy
  [2]: https://wordpress.stackexchange.com/help/badges/76/marshal