The ones I want to do on my iPhone.

This is usually because my iPhone dings more, and is connected to an always on network connection + phone network, so it's often the point of first-contact with any specific task/response/conversation/work unless I am sitting at my desk at home already.

And while I am someone who does take a laptop and an iPad with them in a backpack at lot of the time, that's not all the time. I'm not walking around the grocery store with a MacBook anything propped up on my cart. I'm not hanging from a strap on a bus or train with a laptop in my hands. And using a laptop on the couch usually makes my wrists hurt.

You can do a productivity task where you can't just have a MacBook Neo out.

You can’t carry a neo in your pocket or use it on the bus