As noted previously, SQL itself doesn't care.

What does sometimes care is antivirus (not to start a thread on good idea or not, just that some shops do run AV and should be aware of this).

They can ignore certain file types by extension (either out or the box or by configuration), and it wouldn't know that IDF is a special file to ignore. That file gets scanned and activity to that file gets scanned. It's a non-obvious performance hit.

I can't comment on all AV packages, but I've had some in the past that would have created a problem with IDF.