I only use yeast nutrient on big beers (OG greater than 1.080).
I do add a pinch of sea salt to a lot of beers, thinking that might provide a little zinc. My understanding is that the yeast does not need a lot of zinc, just some.
I suppose if you were a commercial brewer or were under the gun to get fermentation done quicker for whatever reason, you would use it all the time. But my experience has been that it makes no difference in final gravity or taste in low to middle gravity beer.