Security groups for share access, pros and cons?

Hi,

our network shares at the minute are a bit of a mess. loads of single user entries, instead of security groups to set the permissions.

our network has a load of shares, and not much in the the of security groups.

just to clarify it to my self, as i will suggest we clean it up and put some order on it,  what are the pros and cons (if any) of using security groups. 

(i have it in my head, that back up takes a bit less, as there would be less security information to back up. IE 1 security group entry instead of 10  user entry's per folder etc??)

thanks

D