Film grain is effective dither and helps deband a video and can make a big difference in realism. Use real film scans (there are many providers), or get FilmConvert Nitrate and learn to use it. It has a lot of films and options but it’s not too hard to learn. The defaults are ok. Experiment with the grain size and grain strength.
Grain sizes I’ve used (should vary with the video resolution):
480i to 620p 4
Grain strength- you’ll know when you’ve set it too high or low. I’ve been using 60 to 100.
Folks need to use film grain and post their results and settings and/or stocks they’ve used. There is almost zero info on the net about settings folks are using. I don’t think it’s lazyness, but more protecting their “secrets” to give the illusion of a competitive advantage. This is a hobby for me, and even it is wasn’t, I’d still post “secrets”.
In case you didn’t know, adding grain greatly increases the fille size for a given CRF or quality level. Probably one of the reasons movie Bluray data is so huge.