Does using Sleep with FileVault negate some benefits of FileVault?
If you don't require the password when you wake from sleep, then you are leaving yourself open to someone taking control of your data. That is regardless of FileVault.

If you have password set, then the data is still protected from being viewed in a similar method to it being on a locked file vault volume. You can also set a MDM profile to have the FileVault keys destroyed in RAM when the machine enters sleep, so that's pretty much as good as powering off in my book:


https://help.apple.com/deployment/osx/#/iore5b074158


For anything but a highly motivated and skilled adversary (think NSA or FBI) - the extra security you get by powering down the Mac is hard to estimate or differentiate from a locked screen.



That being said, you should turn on FileVault if you have an SSD since there is no other way to ensure destruction of sensitive data other than destroying the key that decrypts data on the drive. You can then decide to sleep or to power off based on how secure you judge your physical environment and the data you have on your Mac from moment to moment.