Ahhh, the subtle importance of ankle mobility: I think the best rule of thumb here is to simply do-as-I-say and not worry about whether you think you do or don’t need ankle mobility work. Everyone needs these drills and it’s best to just go ahead and add them in twice per week.
Adequate ROM at the ankle is required for everything from pitching (baseball) to sprinting to squatting effectively to landing from jump tasks.
In terms of knee health, the body WILL always find the range of motion that it needs! So, if the additional ROM the body needs needs should come from the ankle (like during a high speed cut or turn), but can’t get the ROM from that joint, then it will often ask the knee to provide that ROM. The result? Usually a ligament tear.
Ankle mobility training isn’t particular interesting to dissect, so I’ll keep this simple and refer you to the below videos to learn more:
There you have it another, admittedly subtle, key to Healthy Knees!