Non-Synched Pattern
Non-synced patterns are just regular patterns that can be edited independently. A non-synced pattern can be used and changed over and over without changing or affecting the original pattern.
Think of it as a rubber stamp, to place the Pattern anywhere you need it.
Synched Pattern
Synched blocks are ideal when you want to duplicate the exact same content, text and all, throughout your site. Unlike block patterns, the purpose is to not edit the content within the reusable block. Each instance will be updated at once.
If you detach a synched pattern, it will allow editing like a normal, non-synched Pattern.