If you re-generate the password for each site, rather than sync, it means (1) you can't change your password on that site, (2) if any site puts in the effort to

If you re-generate the password for each site, rather than sync, it means (1) you can't change your password on that site, (2) if any site puts in the effort to brute-force guess your password, they will have access to all the sites you visit. This is not a good idea.