When you delete a user, it will be removed from your account, but you will be able to reactivate same user later at any time. This means that you don't have to add a user again with same email, but to reactivate and send new invite.
Also, when a user is deleted, the seat will remain available until the end of the current billing cycle, but you will be charged at the beginning of the new cycle per actual number of seats (learn more how it works here).
The reasons on why we're not completely deleting a user are so you could reactivate same user at any time and to keep all analytics associated with the removed user.
Pro tips
When a user is deleted (removed) all leads previously assigned to removed user will be automatically reassigned to account owner (Super Admin).
Account owner will be able to reassign those leads to different Closers (hosts) by going in 
Global Data → opening a lead Contact card and assigning new Closer owner. This action is not mandatory, since the ownership will be automatically assigned if a lead schedules a new call with active users.
