Since D&D 4e's release, I've had a hard time understanding the purpose, benefits, and execution of minions as well, especially across tiers of play, where I think their execution fundamentally changes. Surprisingly complex in some ways, but a fresh, great new monster mechanic in the game.
At the most basic level, minions need to add to the cinematic butt-kicking the party gives monsters while being able to pose a minor threat, not zero threat, so that's how I try to play them. That's what's so hard about it... being so frail, they might not have that chance. They die before they get to go sometimes, and though that's not alway satisfying for the DM, it's typically fine with PCs. Especially when there's bigger fish to fry anyway.
What I have learned in running my new primal campaign