If I generate addresses with
m/44'/0'/0'/0', m/44'/0'/0'/1', what is the difference compared with
It indicates that hardened derivation should be used for that step.
BIP 32 specifies a "hardened" derivation method. This method is different from the "unhardened" method in that it requires the parent private key in order to derive the child private key.
For example, the path index
44' indicates that the 44th hardened key should be derived.