Fused switches...where do they go?
In the UK Fused connection units (FCU for short) are used for a number of applications including but not limited to.


Providing over-current protection for a spur that serves multiple sockets or is wired in smaller cable than is allowed for non-fused spurs. 
Allowing a spur to be switched on and off.
Providing over-current protection and/or switching for fixed appliances.
Providing over-current protection for lighting that is fed from a socket circuit.


The first thing I would do is look to see if the FCU has an open flex outlet hole (either on the front or on one of the edges). If so then it probably means that the FCU used to feed a fixed appliance that is no longer present.

If not then I would look for any equipment, sockets or flex outlets in the vicinity. Especially sockets that are in unusual locations (high up, under a counter etc) and test if those sockets are controlled by the FCU. 

If you feel confident in doing so then removing the FCU from the wall (with the power off of course) and looking at what type and size of cable (if any) is connected to the load terminals may give more clues. Looking at the fuse may also give a clue, a 13A fuse likely means sockets or a high power appliance, a 3A or 5A fuse likely means lighting or a low (electrical) power appliance.