Still wondering why this is default on and not off ?
Because when it's off, if you duplicate/copy+paste Controls within a document because you want more of a particular Control or set of Controls, it doesn't increment the Control IDs of the new Controls. Copying Controls within a document and wanting them to get their own Control IDs is a more common use case than wanting to copy Controls between documents while preserving the Control IDs, which is why it's enabled by default.
Mark as Solved.
Just renamed the thread and moved it to "How To" ;)