+100 from me too.
The above example may look very “constructed”, here is another one:
I have a custom “Image” field group with a few settings. I want to be able to insert this on a page in different field groups. The only possibility is to create the necessary fields multiple times.
In this case it may also be possible to register a new field type (with hooks, don´t know if that is supported because I had no use yet), but there are other examples there this is very useful.
