Actually, IIS automatically restarts the worker thread once a day by default; meaning most developers are unaware of memory/resource leaks that don't end up causing a crash within 24 hours. Got called in to look at quite a few "random" issues that turned out to be resource leaks that only showed when the site was under enough stress for it to hit the brick wall within the 24 hour recycle period.

The default IIS app pool elapsed time based recycle interval is 1740min, or 29hrs. 29 being the smallest prime over 24. Seriously.

Yup, and for good reason. It means your site won’t be down at the same time two days in a row.