Difference between implicit enhancement and Pre/Post/Override methods

[#1]

Hi Guys,

I have a question regarding modification.
Could you please tell me the difference between an implicit enhancement and the Pre/Post/Override exits?
With an implicit enhancement I am able to add my own code to the start or end of a standard method.
But couldn't I just use Pre- or Post-methods to archive the same result?
And what solution should be preferred?

Thanks
Chris