In my game, the party healer is a Hospitaler paladin, his combat abilities are vastly sub-par (no casters in the party, so he is clearly outshone by the other characters). To compensate for him being there in a support role, I authorized the leadership feat, something I had restricted from other characters.
His cohort was a sorceress, and as the party lacked any other casters, she became a limited source of buffs and nukes ( I found it perfect that haste and fireball were the same level) and collaborated with him on her spell list, for a support character that rarely ever shown in the spotlight but was always useful and welcome, and most importantly, never despised by the other characters.
I have used the leadership feat a lot with varied results, and the issue always came back that the right cohort could make party members feel redundant or unnecessary. Having cohorts that fill other roles, or supplement undesirable ones tends to be best.
As to followers... adventures are deathtraps. At most, I've seen a dozen followers taken on an adventure to watch after the horses, or escort the npcs, carry treasure, secure a village, gruntwork the pcs don't want to do, which makes them welcome. It's easy to toss a sack of coins at some villagers and tell them to do something, but my players tend to value the honesty of followers compared to hirelings.
The player on the other hand, gets to feel empowered by his choice of feat. Whenever the inevitable "so what's your AC, anyway?" contests start to break out he can always smugly talk about how many and how well equipped his army of followers are, etc, letting him still feel valuable and on par with the other players.
If you stack leadership onto an already highly optimized character with plenty of resources, or an animal companion, etc, it can be abusive, but applied correctly with conscientious players, it can enrich the campaign immensely.
