What do developers need a desktop for when laptops are both portable and can act as desktops when you plug them into a docking station? Is the ability to have

What do developers need a desktop for when laptops are both portable and can act as desktops when you plug them into a docking station? Is the ability to have an easily expanded computer that necessary? Even for a lot of "pro" use that is hardware intensive, like music production, is pretty well-facilitated on a laptop these days. I don't work with video, so maybe that's another story.