User Groups are a great way to group and title a collection of members within your Organisation and assign a Team Leader to the group. When a User is a assigned as a Team Leader for a group, whenever a User within that group marks a Project as Quote Ready, etc. the Team Leader will be notified of this change.
An example of this could be all you assign Estimators within your Organisation to a User Group called "Estimators" with your Estimating Manager assigned as the Team Leader.