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.

I did opt for a knight in the end. Having someone heavily armoured who can hit hard and level fast (at least compared to the fighter/mages) isn’t a bad thing. Plus they can help out with clerical duties once they have some xp under their belt. The equipment you get from the tomb is nothing to be sneezed at either, I guess.

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.