Mostly just curious. I recently wrote my own pagination script which was obviously more then it needed to be. I found this property and it solved all my problems. On my index page I was limiting the number of posts shown to 5 (showposts=5), but I wanted, at the bottom with the pagination to display the total number of pages, like PAGE 1 OF 10. So I stored the query request
$theQuery = $wp_query->request;
Then I stripped the LIMIT from that request, as it was limiting to 5. Then re-ran the query without the limit for the sole purpose of getting the total number of posts based on my query. A lot of work and database stuff for nothing.
I did not realize the wp_query object had that property stored.