I don't use clamshell mode. I have my 2018 15" MBP on a stand and open on my desk so that I can see the screen; it sits adjacent to a 24" LG 4K Thunderbolt 3 monitor. I use the monitor for everything, especially editing photographic images, and I find it handy to check the MBP screen to see how the image looks on that smaller screen. What may look fine on a 24" screen may be a bit too dark on the smaller 15" screen, not to mention on a small iPad or iPhone screen.
Aside from that, the primary reason I prefer to keep the machine open when using it is to prevent heat issues. I use a separate external Apple BT keyboard and Magic Mouse II so that I don't need to type on the computer itself. This setup works for me....