For me the most useful features of Plot over other libraries are the declarative transforms: bin, stack, map, filter, etc. This means that a lot of the data munging that you would normally do before passing things off to the plotting library are done by Plot itself. Why would you want that? Well these transforms are now "facet aware" - if you want to facet on some some qualitative property, slap a `fx: property` on your mark and your transforms will then be run for each subplot.

Secondly, I simply find the API to be very tastefully built. The Geo API (https://observablehq.com/plot/marks/geo) is a particular highlight. I've used Plot for about 1.5 years for recreational side projects - it has genuinely kept me entertained for many hours in no small part due to its interface design.