`createWithSeed` vs using a PDA with f`indProgramAddress`

1. In what situations would I want to use createWithSeed function vs deriving a PDA address.

2. Why do the two generate different addresses

const programId = new PublicKey("4mFDYND4AVREYEJXCPhjq1LnbjELHHebJqG3NZechA7X");const address = PublicKey.findProgramAddressSync([], programId)[0];const add = PublicKey.findProgramAddressSync(    [address.toBuffer(), Buffer.from("anchor:idl")],    programId)[0];// CuisJpFYLe18u7T14Z9kRKveJqFPRb3XwfR7Jh1xo8Kgconst createdAdd = await PublicKey.createWithSeed(    address,"anchor:idl",    programId);// 44nqWMbW4Rgm1q2VddgJJUTFZYAqHsmXETfupaKNxzDN