Because it's a handy way to switch off an appliance without having to unplug it.

My other half always switches off before unplugging. I try to follow her example for safety. Unmoulded plug halves are held together by a screw which can become loose, so when you pull the top half it can become detached leaving the innards within reach of your fingertips momentarily. Given this, I rarely specify unswitched sockets  

You may wish to leave something plugged in so it has a socket reserved and is already to go and then power it up ? It is however another attack vector for grit and corrosion to mess  up your electrics, so not so bright on an extension lead outdoors.

Certainly in our house the switches  get a lot of use and the plugs stay in for months if not years at a time.

At my place of work however, ostensibly to prevent switching off the wrong thing, we do not have them on the lab benches, It leads to a lot of stuff left on overnight in error ,  and a fair amount of unplugging the wrong thing...
Mike

The original reason for switched sockets as I understand it was historical - it started back in the day when many supplies were d.c. and not all appliances had an internal means of switching off. Breaking a d.c. circuit can produce a quite impressive arc (there being no zero crossing point that automatically extinguishes the arc every 100th of a second as with 50Hz a.c.) - which is quite disconcerting as well as damaging to contacts. So switches were supplied and people soon got into the habit of switching off before unplugging 'for safety'. As things moved over to a.c. the habit of switching off was already ingrained so the general public expected switched to remain. For higher rated sockets (>32A) it's still usual to have switches on sockets for the same arc preventing reasons - often interlocked to make sure.

   - Andy.

That said Andy, IIRC (and I may be misremembering, it was a long time ago!) the old round 15A and 5A sockets in our house when I was young were unswitched? I think it was when we moved to 13A sockets that we had switched sockets?

Personally I'm all for switched sockets, for energy saving in the house, and for making sure lab equipment is actually turned off back in the days when I ran a lab. (And still at home in the workshop for avoiding that nasty moment when you move the circular saw and accidentally press the trigger...) Of course we did always have to have the signs in the lab ready for use "Test in progress DO NOT TURN OFF!!!" Which occasionally worked

the old round 15A and 5A sockets in our house when I was young were unswitched?

Quite possibly - there have been both switched and unswitched versions for quite a while - I suspect by the time we got to 3-pin (i.e. earthed) sockets most places were on a.c.

My grandmother's house was like an electrical museum - she had something from about just about every era since probably 1900 - the kind of place where you can tell by looking at the meter that every electrician for the previous 60 years has taken one look at the existing and thought - I'm not touching that - as every addition had its own fusebox and connected straight back to the meter. I remember all the 2-pin sockets were switched in some way - some looked almost like a old round lightswitch, but had socket contacts on one side - others were simple bung shaped sockets, but always had switch next to them on the same wooden backblock.

   - Andy.

OlympusMons said:

Given this, I rarely specify unswitched sockets

There seems to be little point in having a switched socket behind washing machines, dishwashers, etc. under the counter.

There seems to be little point in having a switched socket behind washing machines, dishwashers, etc.

I also prefer unswitched sockets for a few particular applications where you'd prefer someone to 'switch off' somewhere else, or not switch off at all. While switched sockets are the 'norm' however, the economics are such that unswitched sockets are usually rather more expensive than the switched ones despite the extra materials and complexity, so value wise they're likely to remain.

  - Andy.

I fit switched sockets simply because someone may plug in a faulty appliance. I don't like the idea of holding the plug of a faulty appliance whilst inserting into a unswitched live source of energy. (Note: I would not purposely plug in an appliance with the prior knowledge that it was faulty! Just pointing out the obvious in case...)

In general I support the use of switched socket outlets.

Firstly switching off is easier than pulling out the plug, and saves a little energy by avoiding standby losses in appliances that would otherwise remain on forever.

Secondly in the case of portable heaters and cooking appliances, turning off at the socket outlet AND ON THE APPLIANCE is somewhat safer. A child or pet  or confused elderly person might accidently turn the appliance back on, but is most unlikely to operate BOTH the appliance switch AND the socket outlet.

And if the appliance catches fire or suffers serious malfunction, then turning of at the socket outlet is quicker than pulling out the plug.

Therefore in my view, almost all general purpose socket outlets should be switched types, with unswitched types only being installed when there is a good reason to so do.