On the Home page you will see two numbers listed - number of users and number of desktop users.
Number of users is the total number of users that are under management. It's how many users you will see listed in the Users module, possibly across multiple pages depending on the number of users. This includes disabled and archived users. It gives you a sense of how many users you are handling in the account.
Number of desktop users is the total number of users that have been assigned a desktop. This includes both VDI and RDS desktops. This number gives you a sense of how many users with desktops you are handling in the account. And most importantly it gives you a sense of expected Azure compute costs.