I personally don't recommend it unless you are treating for ich or something. There are some fish that do well with salt, but there are many that can't tolerate it, like Cory's and inverts as an example.
I know some rainbowfish breeders swear by using salt(because of their respiritory systems), almost on the verge of being fanatical about it, that said most of them can kill a plant upon sight(there words), so i would assume that for some fish (rainbows) it can be beneficial. For growing plants i wouldn't recommend it. It just depends on your particular area of interest.