I always turn off my laptop before putting it in the bag. The laptop may not sleep and remain on causing heat issues. Why risk that just to save a minute waiting for it to boot up?
Although you make a valid point, it takes me too much time. If I would turn it off every time I moved, I would have to turn it off 3 times a day. That takes 3 minutes every day. That's 15 hours a year wasted on shutting down you mac(if you have 60 days of vacation). Ofcourse, that's exaggerated.
However, I do have to wait half a minute just for my macbook to shut down, I actually have to wait for my macbook because it's the first thing to go in my backpack. Half a minute is important when running out of time (because you need to catch the train). And I just want to move on, I don't want to wait for my macbook, I want to have lunch.
If you take into account that all the time me and my siblings have been doing this and none of our MacBooks broke, I think it's reasonable not to wait for it.
Also, your backlight turns of when you close the screen. When it doesn't turn off, you know it didn't go to sleep and you can do something about it. This way, the chances of your macbook heating up is almost nil.
Ofcourse, if you have the time, you can do it. But for me, there's no good ground to shut the macbook down.