This also helps prevent injuries, particularly in falls. We're much more than we think we are, but we perform as we think we are. You take a giant leap and abandon your self-imposed limitations. There's a lot of difference between sharpening an axe and grinding it into filings. He expects folks to have a good day at least once every 10 days - if not they're overtraining.
Cramps have lots of different causes.
You need to consider dehydration, salt deficiency, potassium or calcium deficiencies. You need to analyze your own situation. A heart rate monitor is good for reminding you to go easy on easy days, but you don't really need a monitor to tell you that. What cross training you do, again, depends on your own goals. Cross training is a myth, because muscular activity is so sports specific.