Plants remove metals and nitrogen from the water. This means that they continuously improve the water quality. Plants are a good idea in any tank unless it is being used as a hospital tank. Hospital tanks must be able to be easily cleaned so plants would make the job there difficult. Contrary to what you have read, and I think I have said it in your threads 5 or 6 times now, mollies do not need salt
ever. Mine thrive and produce scenes like this with absolutely no salt added.
Plants are vital in keeping my levels where they need to be. That being said, I have always (25+years, added a small amount of aquarium salt to my freshwater tanks (for mollies in community tanks, to my African Cichlid tank, not only do the fish thrive, but so do my plants). I think it is important to think about what h2o you are starting with and what aquarium salt can do, in terms of GH, PH, and other parameters. Aquarium salt provides electrolytes that are beneficial to many fish. -D