I would never put a socket behind an appliance. A lot of appliances need to go right back to the wall, so it would make them stick out too much past the work top. Last year during an inspection i discovered a dishwasher had been pushed back onto the plug top. Back of dishwasher gets warm and had melted the plug top to the back of the dishwasher. When the dishwasher was pulled forward the plug top was stuck to the back of the appliance. I have a pic I was going to send into PE, I will post it up this week.
I prefer sockets chased to below work top then trunking below. For appliances I prefer to either mount on a surface box then fitter can cut a square in the back of unit or leave cable loop, pull into unit and mount surface box inside the unit. To keep price/time competitive I like to avoid too much chasing . Been doing a lot of commercial lately and I don't miss using my chiseling drill, I wouldn't be upset if I never needed it again.