The iPad is the perfect weight and size for commuting, at least for me.
I never had a real complaint about the MacBook's portability before, but there was a time when I was traveling frequently and felt the need to switch to the lighter MacBook Air; I eventually had to go back to the MacBook Pro when I needed more storage.
The iPad solved the weight-versus-storage issue for me by letting me treat my MacBook Pro like I used to treat my desktop, but with more flexibility.
The MacBook Pro moved around my apartment and went with me to coffee shops when I had to get work done, but it stayed at home any time I had a commute and could get away with accessing files or apps from a self-standing screen that's larger than my iPhone.
Since I have a separate work computer at the BI office, I could opt for the much more portable iPad over my MacBook Pro on a day-to-day basis. In contrast, Tim Cook said a few years ago that he used his iPad around the house and took his laptop to work — the point is, you have options.