Per title. I seem to remember they let you have a chance to control NPCs in some battles in DQoK, and I vaguely remember some optional tomb in CoK or DKoK that would only let you in if you had a Knight. Am I missing anything? Spoilers are fine.

I'm not really interested in the RP side of things; I read most of the 1st edition novels and find them a bit too stupid to live.

I think that only Knights are able to use the Dragonlance as well, which is a pretty overpowered weapon in a couple of fights.

Yes, in CoK, the optional tomb is only able to be completed if you have a knight. The prize is 6 suits of Solamnic Plate, which new characters in DKK start off with. Note that there is a +5 Longsword is a fake +5 during those trials. I tried exporting a character with that particular item when I first played the game on C64 (thought I was clever), until I noticed that my THAC0 did not decrease when I had the weapon equipped.

DKK and DQK will both allow you a chance to control NPCs if you have a knight. I believe it is based on both Charisma and your rank.

Fighters, rangers, and paladins can also use the Dragonlance.

Even in a power gaming munchkin party the Knight has a natural place, being able to control NPC, use the best non-magic armour in the game, and cast Cleric spells.

Just be aware that knights do give some of their money/gems/jewelry everytime they enter an outpost. The higher the order, the more they tithe. You can transfer all wealth to another character right before entering if needed.