I was going to ask the same question--it's helpful to be able to see the totals as you go. Among other reasons, it allows you to figure out where errors (e.g. what side) and allows you to fix errors BEFORE you enter them and then have to go back into the entry and fix it.

Do the developers ever think to consult with actual accountants before making changes, or are changes dictated by purist designers who think that it "looks better" as a straight unbroken line of rows?  The program is supposed to be designed for us, and not for them.