Here‘s a good yet highly subjective reason: noise. I tried a single-machine solution for a couple of years, consisting of a powerful MacBook Pro attached to an external 27” 4K display. The problem with this setup is that Apple’s abysmal fan curves don’t mix well with my sensitivity to noise. It’s a well-known fact that the MacBook Pro will turn into a jet engine as soon as you attach it to an external HiDPI display (or what Apple refers to as Retina).
Ultimately I had to give up, give in, and replace the single powerful MacBook Pro with a much less powerful 12” MacBook and a similarly powerful 2017 iMac. Would I prefer a single-computer solution? Definitely. But when you‘re stuck between a rock and a hard place you have to compromise, and I’d much rather deal with the (much improved) hassle of keeping two computers in sync than a wannabe 747.
Sounds like needless spending.
Curiou if you’ve considered selling the MBP 16” and replacing with 2020 Mac Mini high end model + keeping the 12” MB or … using an external eGPU setup (if that would help) - not sure what work you’re doing.
Others like yourself have mentioned valid reasons …
Originally, and I still do, believe having a decent or powerful MBP connected to a larger 34”+ display (with/out eGPU; depending on each ones needs) would be more cost effective. The FAN noise is well documented … so potentially my original ‘belief’ or thoughts could be better realized with M1/etc chip in the upcoming 16/14” MBP replacements later this year or early 2022.
24” on a 2021 iMac seems far too small but the pixel density and resolution is nothing to scoff at.
Maybe since I’m not a creative - haven’t played an instrument in decades is why I don’t need the power nor see the reason to have more than 1 computer - UNLESS 1 is corporate supplied for work - and you really wish to keep personal data off of it (really we all should). I find this isn’t so important for macOS users; coders maybe but their treatment vs corporate drones is far more superior and light-hearted.