is there a mechanical reason for turning off the auto shut down mode? Seems like it could bear out your starter.. but what do I know? I don't mind it, but seems like it might eventually cause an issue
Certainly the starter is more robust than a "standard" starter - but given that like any mechanical component - it has a service life, the less times you spin it, the longer it will last.
Pretty good info here regarding start-stop systems and what all goes into it.
https://en.wikipedia.org/wiki/Start-stop_system
Ultimately it's a system that helps the manufacturers get to their CAFE mandates. The actual benefit to the end user depends on your situation. If you live in LA and sit at traffic lights that can last up to 180 seconds, you'll see some fuel economy benefit. In my driving environment I rarely am stopped for much more than 30 seconds and the times that it stops the engine and I'm able to go a second or two later is a really jarring experience. My wife hates it and I'm not much of a fan either, so I installed the ASE harness and haven't dealt with the system since then.