Crypto, hashes and password questions, total noob?

Question

I\'ve read several stackoverflow posts about this topic, particularly this one:

Secure hash and salt for PHP passwords

but I still have a few questions, I ne

Answer 1

what types of attacks are these hashes trying to protect against?

That type when someone gets your password from poorly secured site, reverses it, and then tries to access your bank/PayPal/etc. account. It happens all the time, and many people are still using same (and often weak) passwords everywhere.

As a side note, from what I've read, key derivation functions (PBKDF2/scrypt/bcrypt) are considered better/more secure (#1, #2) than plain salted SHA-1/SHA-2 hashes by crypto people.