Whats the difference between a General Template part and a Synced Pattern?

It does not appear that there is any difference between general template parts and synced patterns. I understand template parts can be assigned with semantic HTML <header> and <footer> tags, but it doesn’t seem necessary to have patterns in a separate category. Patterns seem to be simply template parts that are unsynced. Calling them general is semantically equivalent to being wrapped in a <section> HTML tag. So, the whole interface can be simplified by eliminating patterns and having 3 types of template parts, Header,Footer and Sections. The “section” type template part, can then have the option to be synced or un-synced. This is both a question and a suggestion, so given the above, why are patterns necessary?