Unless your data is worthy of encryption, then I would not turn it on.
The risk of data loss is far greater with filevault.
When you empty the trash, you do not gain that space back until you restart, which in itself can become a lengthy business as filevault has to resize the filevault image file, which can take an age. During this time you cannot use your mac.
in my opinion, it is more trouble than it's worth.
If you have specific data to encrypt you are better off to use disk util to make a dmg and storing it that way, imo.