Bottom line: if you have a Core i3, Core i5, or Core i7 processor, you’ll barely notice the impact of disk encryption, regardless of whether you’re using an SSD or traditional platter drive. Is a tiny performance hit worth the peace of mind of total data security? You’ll have to decide, but if you have sensitive data and a newer CPU on your Mac, it probably is.
If you want to enable FileVault 2 yourself, you can do so in the “Security & Privacy” panel of System Preferences. You can even store the key with Apple which can be retrieved by answering some standard security questions, making it virtually impossible to accidentally lose access to your own data if you forget a password or lose the encryption key.