When a man knows he is to be hanged in a fortnight, it concentrates his mind wonderfully
I doubt that Samuel Johnson had first-hand knowledge of staring down a gallows, but he perfectly captures the effect of an approaching deadline. Unfortunately, all too often the mind is concentrated on the deadline itself, rather on the problem(s) to be solved.
Deadlines are a fact of life in software development. And I've been lucky enough to have worked at several companies where the deadline is just another day: it arrives, the software is released, everybody leaves work early for beer. At other companies, the deadline is a source of panic, sometimes starting at the project kickoff.
The difference, as everyone knows, is that the latter companies set unrealistic deadlines: too much work, too little time.
Except that, as I look back at the projects where I've experienced deadline pressure, I don't remember that the schedule or work effort were that extreme. More often, the problems came from confusion: bugs (particularly performance) that weren't discovered until late in the process, last minute questions about how a feature should behave (with different team members having different strongly-held positions), the undiscovered critical feature, or process delays (QA has to sign off, but the QA lead is sick).
There are lots of techniques to attack these problems, with Agile project management attempting to take on several at once. And I think that any or all can work, even those embodying heavyweight process. The only question is whether they reduce the confusion or add to it.