Mar 10, 2015 02:48 AM|Angie xu - MSFT|LINK
Thanks for your feedback.
if you use multiple application pools, AppPools can run as different identities, so you can restrict permissions this way. At the same time if you have a website that has a memory leak or generally misbehaves, you can place it in an app pool so it doesn't
affect the other web sites.
More hints about use additional application pools, you can see discussions below:
Why add additional application pools in IIS?
Drawback to creating a separate IIS application pool for each website / application