You shouldn't need it with beer. I have read this in Chuck's book and Beer for Dummies. Both agree beer should never need nutrients or energizers.
Its common with wine and specific yeast strains used with wine.
I've used it only on cider. I never boiled it either. Never had infections.
It cuts down on the sluggishness of the yeast and the sulfury gas smells that can ruin a cider or wine. It also lowers the risk of stuck ferments and can un-stick them.
My usage has been 1/2 tsp per gal of must. Additions at or after pitching. (per the bottle)