<p>I've found during crunch times I like to work at night way more than during the day. It's so much easier to focus from 10-5 AM since there's nothing else going on outside, websites usually aren't updating much, and nobody else is around to bother you. I just wind up sleeping from 6 AM to noon instead.</p>
<p>My thermo final is going to take around 30-40 hours to get done, and even though I've been in my office since noon, I haven't been able to concentrate on it very well (while late last night I was able to plow through two problems without many distractions).</p>
<p>It's more like hard class --> all nighter(s) --> lower grade. In other words hard class --> lower grade. Hard is obviously a relative term, and a subject that's difficult for one person might be a piece of cake for another. (And also, you tend to want to procrastinate more on stuff that's more difficult to understand/complete.)</p>
<p>The classes I've pulled all-nighters for are the ones that I didn't expect to do amazingly well in. I procrastinated, of course, but the material itself was not easy to begin with. The all nighter still helped more than it harmed. On the other hand, I've stayed up really late to study material that I knew really well, and have kept up with really well. I believed the extra confidence I received going into the exam was worth the sleep-deprivation.</p>
<p>In short: all-nighters aren't all bad. But still, getting just a few hours of sleep is much better than pulling an all-nighter (concentration-span and grade-wise).</p>