Does Conqueror’s Haki have to knock someone out? I know that it’s super rare and basically pitting your will against someone else’s, but would it be possible to do other things with it? (Yes, I’m aware that if your will isn’t strong enough, you won’t KO anyone and that you can fine tune control as well.)
As stated in One Piece Conqueror's Haki (Haoshoku no Haki), whoever possesses it will have the qualities of a king. So you can control and dominate the will power of people and other creatures like sea monsters, who are weaker than the Haki user. By control, it doesn't mean that you can make people to do something. But you can suppress them for a short period of time and someone who can't bear it will get knocked out.
As explained in Usage and Strengths and Drawbacks of Haoshoku no Haki:


The most common usage of it shown in the series so far is using it to exert the user's willpower onto those with weak wills and rendering them unconscious.

One can also use Haoshoku Haki to destroy things as seen by Shanks when he was able to crack a part of Whitebeard's ship using his Haki.

Another advantage is a proficient user like Luffy can use it to tame powerful and dangerous animals, allowing the user to pacify ferocious beasts such as the Kraken or Fighting Bull.



There are very few Haoshoku no Haki users. Only one in several million people have this ability. So, we see someone using Haoshoku no Haki very seldom, usually when fighting with a large number of weaker opponents. Someone with a strong will will not be affected. We might get to see more use of Haoshoku no Haki in future.