So here are the reasons why I personally like having a desktop.
* Quiet under full load. Can actually run jobs overnight in my bedroom (e.g. rendering, machine learning).
* Frees up space from the desk. Better for ergonomics if you set things up right.
* Can have more memory for memory-intensive things (VMs, rendering, machine learning, etc).
* Slightly cheaper for the performance.
In return, you sacrifice portability. If you try to solve that by having a desktop and a laptop simultaneously, it will probably be painful synchronization-wise. E.g. on your laptop, you're comparing some products - you have excel open as well as a few tabs in Chrome. How do you automatically shift everything over?