I'll have Dreamweaver or Visual Studio Code on the vertical monitor on the left and a browser or Photoshop on the right.
Other upgrades are another 2GB of RAM (6GB to 8GB) that was bought about four months ago, a docking station, drawing tablet, and a 500GB SSD.
My laptop is a 6th generation i5 and didn't have any lagging problem outside of maybe using Photoshop, Illustrator, and a browser at the same time. But I've wanted a SSD since adding one to my old laptop. The difference in speed was night and day. That PC was okay, but it was pretty good once it had the SSD.
The vertical monitor is 19" which seems like it's about the right size. It's long enough to give more vertical space but not so much that it's inconvenient, as in having to scroll my neck a lot up and down to scan the monitor.
It's been really helpful for using Google Chrome's Inspector tool. That's usually on the vertical monitor where it's easy to modify the CSS and then notice the changes in the browser on the main monitor.
And doing this without having to switch apps helps.
It didn't seem that switching apps took up a lot of time. But since switching to the new setup, making changes to code seems easier and goes by more quickly.