Sometimes you write a script that needs to login to a website. Your first thought is "*sigh* Now I have to figure out how to store my password in a plaintext file somewhere". That sucks.
An alternative exists: If the script runs on the same machine that your main browser is on, the script can just copy the session-cookie from your browser's files. This is really useful in three ways: 1) you don't have to store your website-password in the clear, 2) you don't have to write code to login to your specific website, 3) the script doesn't have to delay every startup (or, conversely, you don't have to write extra code to cache the cookies).
Modules that are useful for doing this:
Explanations of the cookies file format of various browsers