I tend to ride with my leg off the horse. From the hip all the way down.
This isn't to say I don't USE my leg and seat - I do, but I really have to make a fairly big movement to connect to the horse, especially since I'm pretty tall and I ride smallish horses. My leg has a long way to go to be able to influence the horse.
When I rode with Mary Wanless, it was immediately obvious that my thigh was completely off the horse, as I didn't use it to post and instead posted off my stirrups. Using my thigh - but without pinching with my knee - was a revelation, but also a hard habit to get into. To this day, I struggle with keeping my thigh on (it's especially hard to keep thigh on but hip open in sitting trot!), but my lower leg is even worse.
Enter the idea of "keeping your legs close." I don't need to keep them ON, because that will just cause confusion. But I need them to be more supportive, like a very light hug, so that when I DO need to cue, I can do so immediately instead of having a time gap between when I start the cue and when it actually reaches the horse.
Turns out, having my legs actively (if quietly) engaged is also really helpful in keeping my seat on the horse. In downward transitions especially, or when Leo gets a little quick, I tend to brace my leg forward. This not only takes my legs forward and away from his sides, but because I'm bracing against the stirrups and literally pushing myself out of the saddle, it pops my seatbones off. In that moment, I have no way to influence the horse, either from my leg or seat. It also leaves me in a precarious position, as I am liable to have put myself behind the horse's motion, usually quickly followed by collapsing forward as the momentum catches up with me (stupid physics).