Comment by amalcon

Well, it can be annoying to limit oneself to a smaller under-seat bag. Taking the bigger bag out during the flight uses up even more of the available space. I've generally got nowhere to put it except behind my legs (which cramps things a lot): on my lap doesn't work if I want to actually use anything in that bag.

It's easier to just pack my laptop (plus anything I might use during the flight) in my overhead bin carry-on. It's a real pain to actually get anything out of there, but a paperback book or ebook reader will fit in a coat pocket or small handbag -- and that's all I truly need on the plane. Plus, the airline won't be able to force you to check your overhead carry-on that way since the laptop has lithium batteries in it.