SDK-SP2/SP1

i went onto the fsinsider website and i clicked on the downloads and it has two downloads that say SDK for SP1 and the same for SP2/ what does this do and is it recommended? and yes i have SP1/2
Flight Simulator and other chat
https://forums.simviation.com/phpBB3/
https://forums.simviation.com/phpBB3/viewtopic.php?f=21&t=62287