Simple. Are 15.6-inch devices too big, and do you need a portable machine for outings? If you are not a perfectionist, Acer's 14-inch laptop with eight hours of battery life might be the ideal TravelMate for you.
http://www.notebookcheck.net/Acer-TravelMate-P246-M-598B-Notebook-Review.135209.0.html
14-inch laptops once had a screen with area 95 sq in and height 8.5in; now the screen has an area of 84 sq in and a height of 6.9in, which is much less useful for many business purposes.