I pitch Fermax with the yeast as the fermenter is filling. I don’t know if I could taste a difference with or without but the fermentation seems to start faster, be more active, and finish quicker with the nutrient that without.
I recently ran out of Fermax and began using WYeast nutrient in the last couple batches. I added it to the boil. The fermentation seems to slowly finish with this nutrient. Of course, both batches used lager yeast so there’s that.
All anecdotal of course.