Let's say an opponent is throwing punches. He throws a jab with his left. You can counter with kicks if you avoid the punch and time it properly, perhaps throw a roundhouse to the body/liver. That can make your opponent hesitate to open with strikes, which could help set up your
punches. Of course kicks can be caught and used either to take you down, or someone can eat the kick and return fire with a punch or two. That's why I would generally throw body kicks off the counter when your opponent is swinging and missing.
Just my thoughts! As I always say I am by no means a pro, but that's my thoughts on countering with kicks. Hopefully some of our resident practitioners can hop in with their thoughts.