Salvinorin always seems like a hack to me...or a cheat code.
I think salvinorin allows you to 'detach' your mind/imagination from your body, and allows you to perceive from a level 'behind' the normal, everyday perspective of your eyeballs. It's like normally we are forced to look through a periscope viewfinder that is attached to our eyeballs and can only see what's 'out there'. But salvinorin allows us to take a step back from the viewfinder. In my experience, this seems to show me my imagination. This is more obvious with low doses and quids than with big doses of extract. Extracts can pull you away so fast that you can miss the initial detachment.
Salvia also gives you more control over your physical body...from a deeper/more central level.
As to the *why*, I can only guess that similar to programmers coding in backdoors/cheats etc., at a deeper level we wanted to give ourselves a tool/cheat/hack to step back a level to be able to take advantage of the abilities available in that space.
Salvia quid enthusiast