Sleep is your body's opportunity to rest, repair, and recover from everything you throw at it. Consistently failing to get enough sleep pretty much guarantees your entire life will suffer, even if you're loathe to admit it. Darin Hulslander, a certified strength and conditioning specialist and nutritionist, says, "Sleep provides mental, hormonal, psychological, and physical recovery. It isn't just a physical need; it's physical, hormonal, and neurological."
In other words, you could actually be a better athlete and a better human being if you just let yourself have another hour or two of rest in the morning.
It's not an either/or proposition, really
When it comes to sleeping in, I'm 100% for it. I hate mornings. You will not see me at the gym before 10am. Ever.
But I'm also 100% for fitting in exercise during your day, no matter what. It's not about sleep OR exercise, it's about sleep AND exercise. The two have a symbiotic relationship where one improves the other, and vice versa.