I use a laptop because I want the flexibility in being able to easily modify my route each day. I don't want to nit pick where I place the dot on the map when I choose a point. Pretty much all the apps won't let you move lines around on the the screen, so you better nit pick your point placement when choosing a point. If you don't know the area then you better hope your right. I always move the lines around, because I can, because I use a laptop. I also want the laptop because I have several program that I use daily which I have written myself and the only place to get them is on my computer.
Yes, when I'm tripping, I'm riding 115-125 miles a day at 14.5-15 mph average speed. This still gives me 3-4 hours a day to plan out the route for the next day and do other surfing online.
Cell phones are way too limiting, and tablets aren't much better.
No I don't use the laptop for reading books. Mostly for checking the weather forecast so I can route myself around the weather so I can stay as high and dry while I am gone as possible. I also use it for staying in touch with family and friends. Some people won't let you get disconnected, unfortunately or I would go disconnected. Mostly I use it for route planning as my trip plans always blow up in my face right before I leave and I have to start over from scratch the second I leave from home, so I am always planning on the fly from one day to the next.