Like most on here I had always thought it to be an utter pointless waste of time.
But my new Merc has it and I actually quite like it! Very convenient to open/close the powered boot with a kick as well as open/close the doors with a simple touch, works really well.
But here's the useful bit. When it's parked up outside your house and the most vulnerable, you can DISABLE comfort access by double pressing the lock button on the fob. The indicators flash 4 times to show its disabled. Brilliant feature on the Merc.
Of course some will say why bother having it if you are going to disable it, but it's useful for any other time you are out and about with your car. It's only really at home where the key could be near the car that you'd want to disable it.