I was looking over an old character I've been saving for when our table revisits 1e. He's a medium, one of the less immediately powerful classes that operates around a very limited resource, but gaining extreme day-to-day flexibility. I like the class because it can access and flourish in all arenas of play, whether that's combat, downtime, or exploration. They can even access 6th level spells from wizard, druid, and cleric, in addition to getting a spicy Wish capstone.

When a medium hits 5 Influence by using one of his many, many influence accruing abilities, he becomes an NPC under the GM's control. Now, that sounds really bad, mostly because it is. But most GM's are... probably not going to want to fully pilot a full PC in addition to everything else, especially not one so complicated as a medium. For some tables, that's enough to just soft-ban the class, but others might find some balance between player & gm control to keep it going. That's not really the point of the post, however.

The medium doesn't have a cap for their influence points - they just become an NPC at 5 or more. If your teammates included a pretty good face to influence the NPC to tag along for the rest of the day, there isn't really anything stopping the NPC Medium from just... using all of the influence abilities at every opportunity.

You can only Spirit Surge once per round, but there are a few other abilities of note. A trickster NPC can steal the buffs from any and everyone. Marshall NPCs can Decisive Strike twice per turn to give your team an extra attack and an extra standard action every turn. Archmage NPCs could just use Arcane Surge to cast free arcane spells of up to 6th level every single turn forever. Legendary spirits have some tricks too, and are likely much easier to bargain with than a new spirit each time. Cyricas can provide AoE Freedom of Movement to your whole team all day long. Stavian can double up on AoE healing or deprive enemies of heals going their way. Darolnyr can swift action teleport you and give the free spellcasts from archmage.

This is likely in no way practical information, I just thought it's an interesting blindspot on all the medium discussion posts I've seen.