I ask for 100 pages when I ask for partials.
I figure that gives me enough pages to see if a book really needs to start at chapter six instead of one, and to see if you can get some conflict and tension going such that I want to read on.
I ask for 100 pages.
If you send 100 pages in Courier, I convert it to Times New Roman, and it becomes 76 pages.
Therefore, a savvy query writer might want to send 100 pages in Times New Roman, rather than Courier. Your goal is to have me read a lot rather than a little. 24 pages is a substantial difference in volume.
If you don't believe me, test it yourself on your word processing program.
And I don't switch to TNR cause I like the smaller font. I change to TNR cause it's darker on my screen and easier to read.