Like anything, Switch Grass has its place.
As everyone knows, it turns non-productive land into a viable field readily with high yield (serious tonnage after a few years to establish itself), and being a warm season grass can be harvested in mid-summer for maximum tonnage for diesel fuel consumed to do so. That is a serious advantage. Unlike other crops that need to be harvested every 21 days for maximum protein, this one can wait.
As others have said though, the animals typically do not graze on it as they prefer other types of grass (alfalfa, timothy, clover, orchard grass, etc), which have higher protein levels anyway, but the reason it is listed as a good forage grass is because it makes excellent silage. Cut to the ideal length of 3/4 of an inch, and ensiled properly, sheep and cows readily eat it. If you use baled hay though...forget it, they will nose it aside in their managers for more preferred grass types.
I have some in my newest field, sown last year and it has done well. It was a low percentage in the mix so the sheep hit the cover and timothy first, but graze some during mid-summer when the other grasses have lost their flavor. The one thing I dislike about it though is that it dies upon the first frost, and maximizing my grazing keeps winter forage costs down. I do have some gravel pits I would like to reclaim, and being less than fertile soil, switch grass might do well there, but as a whole, when shopping for grass seed I'll seek out the mixes with it in higher concentrations so that I do not sow it again.