The best knives for throwing are the ones that have been designed and properly weighted for it, you know, throwing knives. Knives that were created with the intention of being thrown. When throwing with a knife or dagger that is not for throwing, one must work to actively counter the uneven weight distribution to ensure that the pointy end goes into the target. Otherwise, it will harmlessly bounce off their chest. (It’ll hurt some, but hey, it’s their lucky day as you just gave them a knife!)
In the sub-spectrum of knives and daggers, it’s important to remember that there are many different kinds and each weapon has it’s own unique weight even ones that were forged to be identical or created by machines on an assembly line. So, every time a character throws a knife, they’re going to have to adjust to it’s weight and point of balance. If they are practiced at throwing, then they may do this automatically but it’s a good idea to give the nod anyway because it will lend a sense of realism.
Secondly and most importantly, despite it’s recent popularity as “the skill” in the YA genre, throwing a knife has very limited practical combat applicability. In the long run, the knife or dagger will be more useful to your character in their hand than it will be in some schmuck half-way across the room. The schmuck may be dead, but now your character has lost their knife. Depending on the setting they exist in, a well-crafted knife could be expensive and hard to come by. Even when using general throwing knives, every knife lost is one that they’ll have to replace and that can get expensive, fast. Most characters aren’t going to have time to go scouting through the bodies of the people they’ve killed looking to get their knives back and will view any knife they throw as an acceptable loss.
Unlike an arrow, which can’t really be used as a weapon (or makes a useful one) when not on a bowstring, a knife can be picked up by the enemy and used by that enemy against the knife’s previous owner. If you’re going to give your character knife throwing as a skill (but it’s weird when it’s knife throwing but not knife fighting), then this is an important concept to keep in mind.
Knife throwing can tell the reader that a character is comfortable with their knives, was possibly in a lot of situations where they were very bored with their knives, or they are living in a time period where they need to be able to conceal a ranged weapon and guns are not available. However, throwing knives is a tertiary skill, not primary one. You can’t really substitute archery for throwing knives and vice versa.
One of the qualities about the first Assassin’s Creed that I really liked was the mechanic of having to find new knives after I used up all the ones I was carrying. The game gave me two options: travel all the way back to the Assassin’s home base or pickpocket the local brigands. It was a nice nod to the fact that weapons do not self-replicate automatically and an important one to keep track of.