Most people ran SM/Ruin for raiding purposes. SM stands for shadow mastery in the affliction tree. You picked up raiding QOL talents like improved lifetap along the way to shadow mastery.
Ruin is down the destro tree. Since there is a debuff limit, locks can not dot the boss outside of maybe the lucky couple that get to put on corruption for nightfall(affliction talent) procs. Locks will be shadow bolt spam bots in raids until you go oom and then you lifetap to refill mana and repat shadow bolt spam.
So your entire spec was revolved around buffing your shadow bolt damage with shadow mastery and ruin. It worked decent enough in pvp and farming world mobs as well.
Other specs was going deep into the demo tree for soul link to beef your survival. Your shadow bolts didn't hit near as hard but your succy did a ton of damage. Problem is that your succy dies every time the boss farts. If your succy lived long enough though it was a very viable build for all content. Just very difficult to have it live in raids.