Your Capitan License provides your website with a bandwidth allocation, which is much the same as a data limit on a mobile phone contract. It's the amount of data which is transferred in/out of your website each month.
If your website exceeds the allocated bandwidth for 3 consecutive months your subscription will automatically upgrade to incorporate the boosters required for the new level of data transfer.
Information about allocated bandwidth can be found here:
Check allocated bandwidth for Capitan Individual License
Check allocated bandwidth for Capitan Enterprise License
Check allocated bandwidth for Capitan Charity License
Information about increasing your bandwidth can be found here:
How to increase my allocation. Booster: Bandwidth
How to check your allocated capacity and usage:
Login to Capitan and to to "Settings", you will find your license usage and capacity on the right hand side of the page.