There are two types of conventions.
Type A conventions: "please do these, it is better"
and Type B: "please drive on the right hand side of the road", while it is okay to drive on the other side, as long as everyone does the same way.
There's no such thing as a separate team. All code in a good firm is connected somehow, and style should be consistent. It's easier to get yourself used to one new style than to twenty different styles.
Also, a new developer should be able to respect the practices of existing codebase and to follow them.
