Whenever an additional license is assigned to an existing account, this event will trigger.
According to the "Principle of Least Privilege", users should not have access to services they do not require. It also helps you control license costs.
We recommend auditing your licenses regularly. To do so, a detailed snapshot of your tenant’s licenses is available in Advanced Report. User Licenses report lists all your users and the license assigned to them. It is a great way to audit your licenses and control your cost, as you see how long ago the user was connected, and what licenses are assigned to the account.