The problem with being overly busy is that when the deadline is reached there is always this little bit of extra effort you need. You might have finished that paper, but in order for it to be validated, you will have to reread a little or do a bit of extra research. Mowing the lawn may tidy up your garden, but you need to rake the grass together for it to be perfect.
Case in point: my deadlines. I was relieved to find that the deadlines for the guest subjects were actually 2 weeks later than originally anticipated. This gave me room to breathe and relax a little, but also meant that I will be tense for two weeks more.
I disagree with Douglas Adams. I hate deadlines. I hate the stress they bring, the pressure on the quality of your work and the lack of nice whooshing sound they make when passing by. It screws up your life and gives you nothing in return. I just need two more weeks and then it's over.