I work at coffee shops and airplanes. Having 24 hours battery life so I don't even have to carry the power adapter is my dream. You could easily trade the weight of the charger with more batteries in the laptop (You will end up carrying the same weight in your bag) I want to charge my laptop the same way I charge my phone: while I'm sleeping.

The scenario where you're on a long flight and need to heavily use your laptop to catch up on things, or just pass time.

The scenario where you forget to plug it in at night, and don't realize it until you're ready to head out for the day.

Just to name a couple. And both of these scenarios have happened with my phone, which has arguably better battery life.

At university I move around a lot, and often there isn't a power plug because tables are out in the middle of rooms or something. I could try and sit next to a wall or something, but why bother when battery isn't a concern.