The purpose of account credit

I'm new to FreedomPop. Just recently I downgraded my plan to the free one and of course I had to top up my account credit with a $5 charge. So right now I'm left with the free plan and $5 in my account. But what can I do with this account credit? I've turned off the auto top-up, so is there anything I can buy with the $5 credit, or is it just going to stay on my account as a "protection" as the Freedompop says? All of the premium services such as the VIP service or the 1GB plan cost more than $5.