There are good reasons for and against.
For: Protects against a child, guest, repairman, thief, etc accessing your personal information or what not.
Against: Small I/O performance penalty, risk of loosing data if password forgotten.
It really comes down to how confident you are on restricting physical access to the device vs how important your information needs to be kept private. I concluded I only needed filevault active on my laptop. Someone else might conclude differently.
If you have a HDD it depends on what you value more, performance or privacy. Whole disk encryption could be overkill if you don't have anything on your computer. That isn't typically the case but is a possibility.
If you have an SSD I would encrypt the drive.
You may just want to wait for High Sierra though. Native encryption and its expanded somewhat with APFS.