Even if “not 100%” of protein is used, you can still reliably stimulate MPS to sufficient/optimal levels simply by consuming sufficient amounts of protein with a solid leucine content. Sure, it could help with subpar protein sources, but, personally, I’d prefer to just have an optimal protein source; whey, eggs, chicken, beef, pork, fish, etc. I think chicken is very easy to eat. Eating <0.5lbs of chicken shouldn’t be overly difficult. Also, if you’re trying to put on weight, eat real food. Things like beef and eggs are high in protein AND fat/calories. It is illogical to try to bulk eating low-protein foods and supplementing with this multiple times. Just have some nutrient dense foods with sufficient protein content.
So potential uses would be taking it with a suboptimal amount of protein and/or a suboptimal protein source. It’s questionable exactly how much it’ll do when added to a sufficient dose of quality protein. Perhaps it could help a bit with pushing MPS a little more or digestion (perhaps depending on the source of protein), but I personally don’t see the value being worth it for this last use.