Modern laptops are light, powerful, and maintain a charge for a decent length of time. So why would you ever consider buying a desktop? Special applications aside desktops still have some advantages. They tend to be cheaper, more powerful, have bigger storage, are customisable, and anyone who’s ever had an annoying line on their laptop screen will agree, last longer.
There’s one more: you leave your desktop where it is, so when it’s off, so are you.