The downsides are the obvious extra cost for the laptop. Less obvious is the maintenance.
Every few years I will spill a drink on my keyboard. If it's an external keyboard I can repair it or replace it easily. If it's a laptop it could be catastrophic failure. Yes I know I can attach keyboard to laptop.
Then there's the laptop screen, it is easily damaged when traveling. Sometimes the damage is minor. My laptop screen recently started having problems, sometimes it works, sometimes it flickers, sometimes it's just a black screen. External monitor is currently attached, but that's a poor mobile solution. Replacing an external monitor is cheap. So, I found a website that can sell me the replacement monitor. I have to decide is it worth repairing or should I get a new one. Cost of repairing is about 1/3rd the cost of a brand new equivalent laptop.