To add to the topic, hard drives are still worth it if you need vast amounts of space for the cost and the data is something you don't access frequently or is data that doesn't have high bandwidth requirements. For instance, there's no point in putting music, pictures, or movies on an SSD if performance is your goal since their bandwidth requirements are laughably small compared to what a high capacity HDD can achieve. Even in the case of movies, the whole thing isn't loaded into RAM and the file is likely contiguous or mostly contiguous, so seeking through it isn't much of a problem.
Heck, even for smaller applications like say emulators of consoles from the 90s or prior or system utilities, keeping them on a hard drive won't be too bad either.
I I would like for a review site to do an updated version of this with the full monty of in-game statistics. Gone are the days where games ONLY load data on the loading screen.
If an NVMe SSD drive will save me an extra few micro stutters (over a SATA III SSD drive) than it may be worth it. I don't think any definitive research has been published on the matter though.
I believe most game engines use progressive or asynchronous loading these days to minimize any stuttering. Basically, the game loads some minimum and once you're in game, continue to load assets on the side that pop-in. Not only will this shorten load/initialization times, but if for some reason there is a hiccup with storage when loading some asset, the game won't freeze. It still has enough to keep going. Using GTA V as an example, if you're heading to Downtown Los Santos and the game hasn't loaded in any of the background buildings yet, it's not going to stop and wait for them to load. It'll keep going until it loads in.
I remember doing a test for craps and laughs to see if I could run the game from a NAS over Wi-Fi. It worked fine at 802.11ac, but not 802.11n 150 Mbps. Even then, despite chunks of the game world not visible, the game still ran and all of the collision for the world was still there, indicating that the game's physics knew about the world, but the graphics didn't, which is more important from a reliability perspective.