Fort & Lab Demolition

[Witention]

I have searched and cannot find the purpose of Fort & Lab demolition. Can someone explain this in detail?

Also, when conquering a province with a fort, is it necessary to destroy the fort and lab to help reduce opponent dominion, and rebuild a new fort and lab under my pretenders dominion? I notice when a province is overtaken the game immediately demolishes the temple of the opposing pretender. Not sure if this is something that should be done with the fort and lab.

Any clarification is appreciated.