I'd like to restrict a particular admin from being able to access the "Log Out All Users" button, however it appears there is no built-in way to do this.

I'd suggest adding this to the list of things we can restrict in a future version.  👍

What’s the use case to prevent them using it?

In my specific case, Facebook requested credentials to be able to see how the Facebook Connect app is using client data.   This involves giving them access to the Login & Registration --> View and Manage Login Methods area - and ONLY that area.

When testing the login though, I noticed the "Log Out All Users" button was still available.  I'd really rather not have a Facebook agent clicking that button maliciously or by accident, so I can't comply with their request to log in and review the settings. (I'm currently waiting to see if they complain about it)

More broadly though, I can imagine anyone with a need to delegate specific admin tasks would benefit from blocking this button.   

e.g. someone who processes reports, invoices, 3rd party add-ons (like Drip Campaigns), doesn't need the ability to log all users out.