Aside of desktop computers, there are lots and lots of gadgets that any programmer or coder can use to increase own work productivity. Working on laptops, tablets and even smartphones makes sense. One of the main advantages is full flexibility. You have a total freedom of movement. You can go anywhere you want with your small gadget.
The market is full of different devices from dozens of companies. Their competition is so fierce that it pushes the development of this industry by leaps and bounds. Every new device is better and better. In some 10-20 years we have all the odds to minimize physical materials developing "goodies" of the 21 century.
Does writing code with a laptop easier than working on the desktop computer? Each way has own pros and cons. If saying literally, a laptop is definitely easier to use. The only limit is its battery capacity. We are still limited with old technologies. On the other hand, some scientists are trying to solve this issue. Recently a few brand new solutions were introduced. They give us good hope in future.