Free space is important on any SSD in order to maintain performance. Write performance is where performance is most impacted by a lack of free space, which can affect read performance as a side effect of write latency.
All SSDs have space set aside that is not accessible by the user, which is called Over Provisioned (OP) space. Intel SSDs, have more OP space then some other SSDs do, but it is still good practice to set aside 20 - 25% of a SSD's capacity as (user) OP space.
I'm surprised you have used about 100GB of the 330's capacity with just Windows 8 and your applications. You must use quite a few applications. A few suggestions to free up some space:
If you do not use Windows Hibernate, you can get back ~8GB of space (or whatever your DRAM memory capacity is) set aside for the hibernate file, by disabling Hibernation.
Reduce the size of the page file, or move it to another drive. Personally, I do not use a page file, I have it disabled. The page file is a work around for a shortage of DRAM memory, when PCs had 2GB or less memory. Unless you know you will be using more than your 8GB of memory, having a page file on your SSD is a waste of space IMO.
Do you run Windows Disk Cleanup to free up space? Are you saving old system Restore points that are likely useless?
OTOH, if you are not experiencing a loss of I/O performance, you don't need to worry about this very much, but I would not fill any SSD to capacity and expect it to perform as if it was empty.
Just to you know, it’s not a requirement to leave some extra space on the SSD, but it might extend the productive life of the unit.