Hemlock is used when green, I've used a lot of it over the years. In the summer, you may get splashed as you sink a spike. In the winter, it's frozen. You take a sledge hammer to the lumber yard to break pieces loose from the pile. It has a tendency to split or check and twist as it dries out. Best practice is to get it nailed up, with sheathing and blocking when needed, when the lumber is green. Hopefully, this will help to keep it from warping too much. You still need to be selective with your studs and cut up the warped ones for smaller pieces. When dry, the best nail guns will have trouble with hemlock. Since it's normally full of knotty areas, it can feel as hard as dry red oak.
Hemlock isn't a choice most house builders would make but it's fine for garages, garden sheds and utility structures. It can be inconsistent in size, some 2x4s being wider or thicker than others, sometimes more than 1/8". Along with warping as it dries, it's not a good frame for sheetrock or plaster interior walls since the plane of the wall frame may be wavy.
It's used a lot in larger sizes, beams, cribbing, etc. Commonly used for timberframes in my area. More stable in large sizes but pretty heavy, especially when green but not a lot less when dry. I remember framing houses with hemlock years ago for a contractor that was a penny pincher. He paid for it later. Standing on a second story top plate, pulling up 2x12x18' hemlock rafters, frozen and weighing almost as much as me. Best upper body workout you'll get. Just mentioning hemlock brings that sweet, musty smell of the wet sawdust to memory.