Sinew is kind of unique in that it's chemically similar to the animal glue that's used to hold it down (sinew makes good glue too). Animal glue and sinew polymerise at a molecular level and fuse together (if cured for long enough, they become one - Turkish flight bows were often left for three years to cure). Because sinew is laid down wet it will also conform to the back of the bow, unlike a hard backing. The natural shrinkage whilst curing will also pull the bow into reflex, which is good for early draw weight and arrow speed.
Having said that, there's probably little point in laying sinew on a bow over 60 inches or so because it's heavy and will diminish performance. Short bows require a greater skill to hit the target, too.
I do love making bows with it though
Dylan