The OP specifically mentioned a MPB, a laptop, which are pretty easy and high value targets for theft. If my laptop was stolen, I would be relieved to know that my personal data was safe.

There are additional reasons for full disk encryption too, like ensuring that important system files have not been tampered with. Whether or not you want to go that far depends entirely on your level of paranoia.

For a home desktop, the cost/benefit may be a bit different, because the computer is exposed to less places and people. As with many things in security, you would need to calculate what is an acceptable risk to you versus the cost of mitigating that risk.