I agree about 90% of the time. In my very limited experience they work best after an exchange of hands and a bit of separation. I used a round kick in a fight once. We had exchanged a couple of good shots, I felt his head snap back from a right cross or two and he came back with a palm to the center of my face. I used the space from my getting knocked backward to launch one - he was about 6'2" or taller, instead of floating ribs it hit his hip - still gave me a second and knocked him off balance so I could better appreciate the punches I was receiving on the back and sides of my head from his buddies
. Truth be told there was zero thought involved and I had to piece it together after the fact while I was icing the back of my head - "Hey, I actually landed a solid kick mixed in there!"
In another scrap, a buddy of mine had been bum-rushed by a guy with a heavy plastic snow-brush. He took a couple of solid whacks across his forehead, faded back a step and kicked the guy in the gut with a front kick, with steel toe boots. "It hit something soft and sunk in a bit" was how he described it - again it was all instinct - he was directing it by reflex, no volitional intent. When his man sunk away, he didn't give chase.
I used to train muay thai shin kicks and foot jab - both low, and reverse side kick/stomp. Most of my other kicks slowly got phased out and I deliberately let the instinct to use them wither a bit. Mostly these days if I'm working MA is footwork and low MT blocks. I still keep up on the reverse stomp since it telegraphs so little and barely disturbs the balance. I haven't even thrown a round kick in years.