There is also the chance that it will slow down your computer, especially at startup. Mac OS X does have FileVault as a good security option, which uses XTS-AES 128-bit encryption to password-protect your entire hard drive, but this is a drastic measure to take unless you're prone to theft.
While you may not have loads of secret files hiding on your computer, there might be one or two items that need a little extra security, like a file of website logins or a folder of risqué photos.
