Carb cycling is used by many in contest prep. Some folks swear by it.
I've done it, with moderate success.
My personal preference is NOT to carb cycle. I think I have better gains, and more consistent fat loss when I don't do carb cycles.
I DO think it makes sense to eat more on days you do legs. They, are, after all, 2/3 of your lean muscle mass. I'm not so sure I'm sold on low carb to depletion and then re-carbing and starting over. The thinking is that it keeps your metabolic rate up because you carb back up before you get laggy but I don't buy it.
My personal experience was that I felt drained on low carb days from not eating enough, and sleepy on high carb days. For me, a more consistent diet works better.