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.