As someone who programs a lot, it's worth it (and not that expensive, you don't need high refresh rate or anything). Being able to use spatial memory to navigate between most of the working set of windows, being able to show a lot of text on one screen, etc.
Only downside is that it's surprisingly hard to drive two 4k screens, laptops are likely not going to be happy (or have low refresh rates), even my 3700x/2070-super desktop doesn't like displaying youtube like videos on both at the same time.