I guess it's like fRO than.
If you have over 300 items in storage and your premium acc is running out, you can still remove items from your storage, but you're not allowed to put in any more untill you reach the 300 limit again.
It's a very nice solution if you ask me.
On this way, you don't have to pay for buff accounts or accounts you're not playing much currently but still have full access to them, no matter how long you're online with them.
And if you want to create a new char, well, do it now or use a low premium subscribtion - helps with leveling too.
For servers that are used to be paid the whole time, it's not big of a deal, but a very nice bonus.