Security through obscurity, its about a million times more effective than security theater. If you dont know where a certain companies servers are then it significantly reduces the chances you will try and gain access to them physically, having employee's post pictures that could identify servers increases the risk of them being identified, datacenters are rarely exclusive to one company or another, some companies have their systems in a caged off area, I've seen some that just have them in a rack in an open part of the DC where you can wander around and the physical security is down to the lock on the rack itself. If it did become public knowledge where bank or big business kept its servers they might then be put in a position of having to relocate them which is rarely quick, cheap or easy.
Its common sense really not to post your geotagged image to facebook and twitter along with a checkin and a nice comment saying 'hey guys check me out, just installing new database servers for highstreetbank plc'
As for not being able to take cameras into a DC, the only place i've ever had to actually hand over my phone was at a location where the mini-DC was at the back of a warehouse full of phones and it was more to do with the fact that they were wary of people stealing phones than taking pictures in the DC, If I do a DC install I always take pictures not for showing to people but so I have proof of how I left it, i.e "yes I connected all the FC connections correctly, look see heres the picture" (helps significantly if you have a high res pic and you can visually trace cables)
