Someone asked me, "Should I start a new page after a chapter break?" that is, start the new chapter on a new page, or just skip a few lines and start it at the end of the last chapter.
I think what matters is... do you need this ms to be longer or shorter? :)
Keep in mind that whatever you do, the editor will do it house style. But if you're over 400 pages, well, save the white space and start a few lines down.
Not that any editor is dumb enough to be fooled by page count. Well, I am, but generally we do pay much more attention to word count.
Can't hurt though. It looks like 399 pages? Good!
Remember when books were 550 pages?