It may be a little confusing, but the flexibility is there to do whatever you want. The include and exclude article IDs always has the first priority, so if you add specific IDs to include or exclude, the social buttons will always show (or not). That's regardless of the category setting.
The category setting can be use for more broad settings. So, if you don't want the social buttons to show anywhere except for a select few articles, you should configure it as:
* Category - Exclude and select all categories
* Article Include - whatever specific IDs you want to have social buttons. Even though the parent category is excluded, these will still have the social buttons.
I hope that helps explain, but if you need anything else, just let us know.
Alex