There are never enough!
Every week the colleagues will complain that some pair or rather only works on the left ear, or worse still, that there is some intermittant problem. Soldering is usually the final solution and that can fail too.
Ideally every pair of headphones should be connected to its own output amplifier, but again there are never enough and so it happens that phones are connected parallel. Beware! plugging 32 ohm cheapish walkman type headphones parallel with 600 ohm (semi)profi german or austrian ones will make the 600 ohm headphones very quiet. Turning up the volume will blow up the 32 ohm phones. This happened several times at Radio 100, after the big fusion when equipment was donated from several different groups. First we seperated them into 32 ohm and 600 ohm types and then we made the profi studio of our friendly legal cable radio (although it used to be in an illegally occupied building) exclusively 600 ohm headphone country.
Finally we built and installed seperate adjustable headphone (and record!) outputs in the presenter and guest areas.