[EasyRider]

Can someone please tell me what this is for and how exactly it's used in the Full Mission Builder?

Thanks for the help...

Select all is used in Map Editor ,"Unlocked FMB" mode only.

It selects every object on the map and turns every icon Red.
It helps to select an Icon because in Map Editor to find them,the spot where you click on is hidden in Map Editor.
So selecting all can turn all Icons Red so you can see them.

Or hit Delete when all is selected and every object on the map will be deleted all at once.

But again this is in Map Editor only

Easy