Perhaps they already knew about the location, but were looking for some appropriate cover to protect an asset. Further, the US military may wish to make ISIS fearful of using social media, which has been a powerful tool for them.

Alternatively, the guy in charge of releasing things to the press gains points for doing this, and the guy who loses points by having it released to the press is someone else who didn't have control over it. As with all organisations, there is politics and point-scoring and competing agendas and just plain incompetence.

Well I guess that ISIS selfie guy won't get that promotion after all ...

It also hurts their credibility by portraying them as a bunch of amateurs who a superior force (the US) can destroy with ease.

It depends on how stupid the selfie guy was. He could've accidentally left his GPS coordinates in the EXIF data of the image (many phones do this by default). Not much classified sleuthing required to track that down.

You are correct in your analysis. ISIS's main recruitment source is the social media. So, if the US defense can get ISIS to use less social media, it is a net win.