Question:

What specific function can be unable to use when turning on the 'Blocks apps from unauthorized stores' feature?

Answer:

When turning on the 'Auto Blocker', apps from unauthorized stores is blocked so that only apps from authorized app stores can be installed.

And 'Install unknown apps' menu is disabled, so also apps allowed from those source can't be installed.

You can see more details through 'Learn more' menu on 'Blocks apps from unauthorized stores' in Auto Blocker.