For general purpose sockets the recommended heights are in the guidance notes.
it is all about not discriminating against disabled people.
however in my opinion, this doesn't mean that a socket can only be fitted at those heights, any socket that has a dedicated use should be fitted where it is needed, i.e. behind the tv or above a kitchen cabinet for an extractor etc.
It could be argued that if you put a socket in a difficult to reach location, at the very least you should give due consideration as to weather it would be appropriate to fit a switch (isolator) for the socket in an accessible location.