If you were already carrying a 15" laptop plus full-size external keyboard plus mouse plus power brick for the laptop, a dongle is not much of a burden to add on. And many people who did that with USB-A machines tended to carry other accessories as well and end up with an external USB hub in the bag too.
I have a keyboard and mouse at my desk. I plug them into my laptop when I'm working at my desk. I don't carry them with me at all times, though, and I don't know many people who've ever done that.
