Can anyone confirm that this statement "Select to recycle worker processes after a specific period of inactivity" in this Microsoft help file is wrong and should in fact not have the "of inactivity" at the end of it?

+1  A: 

Yes, that seems wrong. As far as I'm aware, this option just recycles the processes regardless of whether they are idle or not.

This article seems to confirm that too.

Mark B

The statement you quoted is correct. It's a way to allow you to free up resources that aren't being used.

When it is necessary to conserve system resources by terminating unused worker processes, you can configure a worker process to gracefully close after a specified period of time. You can use this feature to better manage the resources when the processing load is heavy, when identified applications consistently fall into an idle state, or when new processing space is not available. You can also start additional worker processes to replace a worker process that is finished.