This should be debated at length in any road or tri forum. It is related to a person's knees, is more pressure put on knees at lower cadence(?), does a higher cadence require less work/distance than a lower one and a corollary as to how more efficient cadence help with the processing of lactic acid in the muscles. (And yes, too high a cadence generally makes you bounce on your saddle. Not good.)

Lance fans will claim that a higher cadence is more efficient all around and proven by 7 wins. Jan (Ulrich) fans will claim that a big engine runs at lower cadence.

I like a higher cadence but I often move around my cassette on the road bike when I'm pace lining. Sometimes lower cadence feels good as well. My guess is that this is my body telling me to move between fast and slow twitch muscles to give different groups a chance to rest a bit.

I am by no means an expert. As I said, hit up a tri geek forum and you’ll find plenty of experts. All disagreeing. That is a start anyway.