Knowing it in principle and knowing when to put that knowledge to work are two different things.
I used to catch *everything* that was going around, including some things most other people didn't. I got sick three, maybe four times a year. I always put it down to having a lousy immune system, until in one checkup I mentioned to my doctor that I'm a pretty loud snorer. "Better have you checked for sleep apnea," he said, and sure enough I had it, although only a relatively mild case. He prescribed sleeping on a CPAP machine, and since I've been doing that I almost never get sick. Maybe once in four years.
Anecdotal evidence, I know, but my point is this. Now that there's research demonstrating the impact of sleep on immune system performance it makes sense to make questions about sleep quantity and quality a routine part of health surveillance. I just happened to mention snoring to my doctor on one visit; if I'd been asked twenty years earlier it would have saved my employers a lot of sick time and me a lot of misery.