I'm not aware of any disadvantages from using it.  I don't use it
regularly.  It was a feature added to help people who are sending their
copy pool offsite for disaster recovery storage.

You need to send your DB backups off site if you send copy pool tapes
offsite- the data tapes aren't readable without a copy of the data base
(and if you use the DRM feature it selects them to go offsite
automatically.)

But if your disaster recovery site is a long way away or you use a
commercial service, it isn't easy to get them back in a hurry if you
need to recover from a data base problem in a non-disaster situation.

And there's not a good way to copy the DB backup tapes so you can have a
copy on site and offsite.

So the DBSNAPSHOT gives you a way to make an EXTRA data base backup, so
that you can leave one set onsite and send one off.

That's the only use for it I know of.