A board is considered “quarter-sawn” when the growth rings run, more or less, perpendicular to the face of the board. Quarter-sawn boards generally have straight grain and are less prone to shrinkage, compared to other boards. These factors don’t come into play with the 2x4s you use to frame a closet—but it does with the shelves and cabinetry you put into that closet; you want those boards to remain straight, flat and stable.
As the comic George Carlin might say, a shop is mostly just “a place to put your stuff.” The physical aspect of a shop is indeed simply a space of some kind — a garage, a barn, a teepee — that keeps the rain, rust, and robbers away and houses a collection of implements needed to saw, plane, slice, sand, and pound raw wood into useful objects. But just like the difference between a house and a home, what transforms a building full of tools into a comfortable workshop goes beyond the mere physical aspect.