For personal use, I have a 27" 5K iMac, with an attached 5K Thunderbolt monitor. I like it for photography, and general computing with two large 5K screens.
For work (now at home during Covid), I have a MBP that I typically use in clamshell mode attached to two Apple Thunderbolt displays and a full set of peripherals (KBD, Mouse, Trackpad). I mostly use office applications, so I do not need the high resolution displays.
For work in the office (zero in the past 20 months), I connect my MBP to a 5K display and a full set of peripherals (KBD, Mouse, Trackpad). I generally keep my MBP open as a 2nd display, but honestly, it feels too small next to a 27" display to be useful.
For my very frequent travel, I take my MBP and my 13" iPad. I have dual logins on my MBP, both work and personal. I use iCloud to keep my personal files synced between my iMac and my MBP, while I am traveling, I have access to all of my data. When I am working on something more complex on my MBP during travel, I will use Apple SideCar to use my 13" iPad as a 2nd display. I also carry a mouse with me. Having the dual 13" displays is actually quite nice while traveling, but in no way does it compare to having dual 27" displays.
One of the biggest reasons that I like to have an iMac at home is because 100% of my data syncs back to that iMac, and from there, it is backed up to multiple destinations including the cloud (BackBlaze), locally via Time Machine X2 (direct HDD and networked HDD), and is also cloned via CCC. I am a strong believer that backups with version history are important.
We used to have dual iMacs at home (myself and my wife). Over time, she used the iMac so infrequently that we gave one to the kids, dropped to just the single iMac and I gave her a login on my machine. Actually, she also has a login on my MBP, so if she needs to get to her data when we are traveling, she can borrow my MBP and get to all her data via iCloud.
/Jim