it's the first thing I turn off when I start the car up.
I believe the featue is in cars to (and this is by no means exhaustive);
- increase fuel efficiency
- reduce emissions
- noise reduction
- less engine wear when idling
- cost savings if the above are true
That said, the disadvantages appear to be (again, there may be others that should be in this list);
- battery wear
- start wear]
- delay in responsiveness
- imapct on your driving exoerience as it can be inconvenient / annoying
- limited benefits depending on your driving habits, conditions or style
- increased maintenance cost
Personally, I feel the disatvanges for me outweigh the advantages, so off it goes. Racing the old lady in the Citroen C2 off the lights when she doesn't know we are racing is less fun when I have to wait that extra moment for the car to start up!