When sending an email, you can exclude certain segments in your Email Details. After all, it wouldn't make sense to send your list of frequent visitors an email pertaining to contacts who haven't attended your studio in a while.
In your Email Details, navigate to the "Exclude these lists" field and select the segment(s) you'd like to include.
*Notes:
Some segments exist by default (ex: "All Contacts").
The excluded segments take precedence over the Recipients list. If contacts are included in the recipient and exclusion lists, they will be excluded.