Mobile devices are very portable and accessible rather than large computers
An advantage, which is the most important is that it is very easy to take with you everywhere. Supplies quick information anywhere you go.
A disadvantage would be it is generally not as powerful as larger computers therefore, it has a lot less features.
A Desktop computer is good at storing storing data.
A disadvantage is that they are usually larger and not as easy to move
An advantage is these usually have more power and features rather than the others.
A notebook is a reasonably sized computer than had good power and portability.
An advantage is that they are a good balance of power, speed and portability. You can take them to other places fairly easily due to their size and they have good power as well.
A disadvantage is their not as small as the mobile devices and not just as powerful as a desktop computer. So if your looking for specific uses this may not be an option.