Why ask why? Well, for one thing, some guys never know when to give up, and I'd have to say that Geoffrey Bennington and I have that in common. He probably got halfway through Derrida's work, just as I got midway through his, and most likely said the same thing I did: 'What the hell am I doing this for?'. I'm sure he gave himself the same answer I did: you started that damn thing, so you might as well finish it. And so it goes.
What it's mostly about when you wander down this particular corridor is the intellectual challenge. As I mentioned previously, most people who plunge so deeply into semantics are like transmission mechanics. They're never going to build a car, so the next best thing is specializing in what makes them work. Face it, academics are largely frustrated authors who only publish books as a job requirement. This is why you can't make heads or tails out of what they write. They rely so heavily on jargon and technical writing that they forget about the poor sap who has to read their stuff. What I suspect is that much of it is smoke and mirrors on their end. Once you simplify what they're on about, you realize that it doesn't make a bit of difference in the real world. That's essentially what most critics of deconstructionism contend.
The book is written in a split-level, with Derrida's ramblings at the bottom of the page in postscript format that, in a disproportionate number of cases, take up as much as half the space. I suspect that the author decided to publish it as a parallel narrative so as to allow us to see the gibberish he had to work with. The Derrida portion is a form of raving madness that seems to be taken from a journal of sorts. Yet Bennington seems almost to ignore it as he takes off on his own tangents, rambling on themes and elements such as metaphors, signatures, translations, femininity, politics, Jews (!) and Other and Being. How on earth do you go from literary analytics to philosophical diatribes in the same paragraph, much less the same publication? Ask Bennington, Derrida and the rest of the deconstructionists. Or, just ask Alice, as Grace Slick of Jefferson Airplane suggests. I think she'll know.
I would recommend this for Mensa patients or those who think they've mastered the art and craft of literary analysis. Other than that, take the advice of the Wikipedia editors who stamped warnings all over their Deconstruction page: in so many words, don't waste your time.