Offline lets you roll over credits you don't use. Each month, you get 2 monthly subscription credits. For each of those credits if you:
Claim something and don't use it before the claim expires
Don't claim anything
... we will roll over the unused credits to the next month.
You can roll over up to 4 credits at any one time. After that, you will not be able to roll over more credits. You will, however, get 2 monthly credits each month so you can possibly have up to 6 of these types of credits.
We also have bonus credits that do not count toward your roll over limits.