You could build both atomic bombs and nuclear missiles back in BNW. And there's some kind of logic behind this: atomic bombardment lowers city population with the same rate, be it atomic bomb or nuclear missile. So if you want to destroy a city you just drop an atomic bomb first and after finish it with nuclear missile. So it takes one less uranium than if you've used two nuclear missiles instead.
Yeah, and if you don't have access to iron when you've researched Gunpowder you probably still want the ability to build Trebuchets, because they are better than nothing. Same thing with Galeasses and navigation. Heck, I would love to have the ability to build longswordsmen for the rest of the game so I could get the free shock promotion from them.
I'm not saying there is no use for this, I'm saying it is following the game's rules.