So, let's talk about why nitro exists...
Nitro exists as a way to emulate the pour from a beer engine, without introducing oxygen into the beer, and spoiling it/shortening the shelf life. Guinness invented nitro for this very reason.
In air, we have roughly 78% Nitrogen and 21% oxygen. Those numbers will be relatively familiar... most Nitro gas tanks are actually 70% nitrogen and 30% CO2. All they've done is simplify it, remove the oxygen and replace with CO2 which as you know does not spoil the beer (oxidation).
In beer, CO2 bubbles rise to the top whereas nitrogen bubbles fall to the bottom when knocked out of solution in the beer by a restrictor (aka creamer) plate in the spout - this difference is what causes the cascading effect. In Cask beer, the mixed gasses (i.e. O2 etc) rise to the top and cause this when knocked out of solution in the beer by the force of the pump and/or a sparkler nozzle.
So, now that we know that, think about all the beer styles that taste great on a cask... it should work pretty good on nitro too. John Smiths/Belhaven Best are examples of best bitters which are now served on a nitro line (although usually this is 60/40 rather than 70/30, but has the same effect, as well as the restrictor plates being a little less restrictive...).
CO2, as someone mentioned above, adds pop/zing to the beer usually. It is useful for sending aromatics up to the head where the drinker can smell them. If you use nitro, it will keep more of those aromatic compounds in the beer, thus dulling some of the perceived aromas. For this reason, I wouldn't use nitro/cask for super hop-forward beers such as NEIPAs.
Hope this helps someone