In reply to Frankie boy:
If you're a climber climbing on a banned crag there's very little chance anything bad is gonna happen. Trespass is not even a criminal offence so pretty much the worst thing that can happen is you'll be asked to leave.
If you write a guidebook encouraging people to climb somewhere banned you are a much easier target - they'll have your name and address for a start.
So guide writers tend to emphasise bans to protect themselves.
Climbers tend to ignore bans so they can go climbing. Pictures of people climbing is pretty much risk free. Even if you can identify the climber you still have to know when the pic was taken and its pretty unlikely anyone is going to attempt to take you to court for such a minor thing.
Some bans are worth sticking to however. If the BMC for instance is negotiating access to somewhere it _may_ be prudent to stick to the ban until the matter is sorted. And also agreed bans on sections of cliffs, most often for wildlife concerns, ignoring such bans risks getting whole crags banned or banned permanently. Hopefully most climbers would actually appreciate conservation measures for their own sake in such places.