As said only appliances requiring local isolation are those with a motor over a set size, it was considered years ago that isolation was sensible for washing machines as before they auto switched off with unbalance it was known for them to have loose weights and roam across the room smashing anything in their way, but today they auto switch off if not balanced. Any other appliance you can switch off at the switch on the appliance.
However the switch is often single pole so if there is earth leakage problems you need another method to switch off the neutral and well as live, but in the main we can drag it out and unplug.
For tradesmen to work on your appliance they must know it's isolated so where you can't unplug having an isolator makes sense, with for example the cooker, however it is common for gas cookers not to have isolators so why should electric? Even when gas cookers are plugged in, you still need it unplugging by a gas safe guy as the sockets often leak and you don't have equipment to test. So no rule saying must be local isolator.
However you do need a method to isolate and although you can get double pole switching single width RCBO's for some consumer units, you can't get double pole single width MCB's to fit the consumer unit, so since technically neutral is considered as live, you can't isolate without turning off whole RCD set of MCB's or whole house.
So it does make sense to have a method of isolation without turning off other things, so cooker isolator although not technically required, it is a really good idea.
Also many fridge/freezers can't be turned completely off at the units own controls, and full of food you often can't move it, so a method to turn off is again a good idea.
So a 13 amp plug must be in free air as it has a fuse which produces heat and needs to cool, the same to some extent with a FCU although some heat can go into the wall you do need to be able to change the fuse. But a simple switch/isolator does not produce heat unless faulty so you could have switches at the back of a cupboard although it would be hard to reach.
Kitchen in this house has a small consumer unit just for the kitchen right by the back door, in real terms there was no need at all for oven isolators, hob isolators, or any others, but the electricians doing the work insisted on fitting them. The hob isolator is always turned off and the RBCO feeding the hob isolator is also turned off, and there is a plug in Lidi induction hob sitting on top of the halogen hob as halogen so useless, so was glad I could isolated the hob.
