Technically there is no difference.
The only difference is that your self generated certificate can not be proved to be trustable and a client can not say if the issuer is truly the identity the cerificate assumes to be from.
Example:
The web site of a financial institute must have a CA approved certificate, because the client doing home banking must know, that he is truly on the web site of his bank and not on a site of somebody pretending to be the bank.
If you only want encryption for the traffic it is ok to use a self generared certificate.
Regards,
Oli
