I'm not always thankful for this particular ability but today I was. I am the type of person who wakes up when the alarm goes off... and usually can't get back to sleep. If I'm woken at the light point in my sleep cycle, forget about going back to bed. I have to be pretty exhausted to fall back asleep.
This benefited me today, as I was sleeping in a little when I got unexpectedly called into work at the last minute to cover for a colleague. From answering the phone call from my coworker, explaining the situation, to me being at work was about 20 minutes or so. I literally leapt out of bed, tossed clothes, shoes, a little makeup, and deodorant on, grabbed my keys and phone and headed out the door. My work is about 5 minutes away, and I made a detour to St Louis Bread Co (aka Panera for those out of town folks) to grab an egg and cheese sandwich and green tea to wake me up and keep me going until lunch.
I was decently alert and managed to be personable (good thing since I was sitting at the front desk) and maintained my energy through out the day. I have gone pretty non-stop since then and am finally having time to breathe.
So while I often curse this ability to wake up at the drop of a hat/pin, I am pleased that it was useful today.