Private browsing in Firefox

Recently I learn about Private Browsing feature in Firefox web browser; it doesn't store any password or browsing history.

First I thought that where I can possibly use it for.
Later I found it handy at work; or I can use it when I borrow my wife's computer or something.

I shouldn't be but it happens from time to time that I check Amazon, check my emails or check YouTube videos. I don't want to store any record of them.