The problem is that if you stick strictly to the manufacturer's recommendations, unless you're only photographing a limited kind of scene, sooner or later you will either blow out highlights or lose shadow detail. That's because you need different development schemes for different subject brightness ranges in the scene. When there is a very big range of light from dark to brightest (long SBR), you have to decrease development in the highlights. When you have a limited range of light from dark to brightest (short SBR), you want in increase development to spread the tones of the scene more widely across what the negative can reproduce.
The whole reason things like Zone System exist is to control the range of light in the scene and "place" it properly on the negative. That way you capture as much as you can on the negative and decide how to use it in the printing process.
For years, I followed manufacturer's recommendations carefully and got a lot of "meh" negatives. The shadows were thin and highlights got blocked. When I took the time to dive into Zone System and learn about development controls, it was quantum leap in negative quality and printability.
Just for fun, try this with a roll of film you don't care a bunch about (because I cannot guarantee this will give you good results).
- Set your light meter to 1/2 the box speed for your film. So, for ASA 400 film, set it for 200, for example.
- Shoot a normal range of light - some stuff in the shadows and some bright highlights.
- Develop the film 20% less than recommended for your developer/temp combo, agitating as usual
See how you like the results when you print.
(This assumes you have a decent light meter and a reasonable thermometer and timer ... if not, all bets are off
😉