Hi a friend of mine is well into apple gear,he gave me a tip today to Turn off FileVault to gain a lot of space.
Should I listen to him?.
FileVault 2 (the most recent version) uses a fixed amount of space and no more beyond the amount of space your data usually takes up when not encrypted. I believe that in no case is it larger than 650MB. However, it might temporarily use more space than this, but it will soon be recovered.
Is it worth turning off FileVault to recover that much space? Folks debate that. Have a look at this discussion:
https://www.reddit.com/r/apple/comments/35c42s/should_i_use_filevault/
That discussion offers some good points. You don't have to be a secret agent to benefit from having your data encrypted. Users often have banking information on their computer, tax return data, credit card data, business records, private correspondence, information that would make it easy to steal your identity, etc. And laptops get stolen all the time.
Personally, I'm in the middle. I don't recommend FileVault, but I think that your important/sensitive files or folders should be encrypted. You can encrypt them with Disk Utility, but it's a bit of a pain to use. This free utility makes the process as easy and fast as it can be:
Crypt3 (free)
https://itunes.apple.com/us/app/crypt3/id413756594?mt=12
http://dekorte.com/projects/shareware/Crypt
(Instantly encrypt and password protect your files or folders. Open them with a double-click and enter the password. Not even the FBI can break this encryption.)