Quick answer, not by much - if at all. I sometimes take out the iPad or tablet to reduce bulk.

The key deciding factor is how & where you plan to bring that personal bag or day bag into (and, certainly not the board room, etc. - trade shows & conferences are fine for me) - I would go with a basic black one. Assumed that you are using the Motherlode TLS 22" Convertible - if & when it is not overpacked & overstuffed, there's plenty of space to fit a messenger bag or any soft-sided shoulder bag on the outside compartment, without excessive compression with the straps - or make it bulky like a whale. My Bag is a smaller one that will fit, very tightly, a Sony Viao 11.6" netbook prefered on most trips (over the 14" Dell) - the "package" is about 3.5" thick - it's smaller than a medium eBag packing cube (loved them & have plenty of them to mix-n-match)

The "S" Classic Bag will easily compress to fit and should be ideal for the MB - just double check the specs. I used nylon/zip pouches to keep some items together, so it's quick & easy to move them around before boarding or after hitting the terminal off the jetbridge - while the TLS stayed in the OH bin in-flight. The tablet is usually all I need for shorter flights along with inline earbuds. I also use a neoprene sleeve for the netbook/notebook, especially when storing it in the "hidden" back compartable to keep them in near new conditions and avoid scratches. Pack your contents into a medium packing tube, it will slip easily right inside the U-shaped zipped section and disappear.

Check eBay for deals, should be pleasantly surprised to find a pre-owned or even new ones without tags for as much as 50% off retail pricing. But, there are times & places where it called for using the good old Coach Beekman briefcase. For urban/weekend errands, the Bag is a better fit vs. shouldering a STM laptop/messenger or other "high profile" ones that draw attention to what's inside.