In IIS 7.5 you can enable the event logging when application pool recycles. When IIS will log, for that you can set certain number of settings. This logging is very important when you want to find out why and when your application pool recycling.
From List of Application pools, Right Click on the required Application Pool > Advanced Settings
From Advance Settings windows > Recycling > General Recycle Event Log Entry
Now, based on configuration setting, during recycling of application pool, IIS will log and entry in Event viewer from Source WAS.
You can set all other configuration value for Application Pool from “Recycling” settings.
This logging is sometime very important if you want to track when and why your application pool getting recycled.