Hi, John. Good question.
If I get two hours less than normal, I feel it in the early morning, which is when I work out. If it's strength, I get through my workout, but noticably more slowly. If it's cardio, my heart rate is about 5 bpm higher than usual. I worry about missing sleep on recovery days, but I can't put my finger on any particular effect. (I very rarely miss meals.)
I do volume day for the Texas Method on Saturday, so I can sleep in an extra hour.