Boats come in a variety of different shapes and styles, but one very simple distinction is denoted in the way the hull connects to the topsides. This area is called the "Turn of the Bilge" and can either be a soft turn or a hard corner. Soft turns are called soft chines while hard corners are called hard chines. Each has its own tendencies and characteristics.
Soft chines are easier to tip and roll around. Sailboats tend to have soft chines since they are designed to heel over and sail on one side of their hull.
Hard chines are considered more stable and are less easy to tip and roll. Powerboats tend to have hard chines as they offer more stability in a boat that is designed to stay upright all the time.
From a construction standpoint, chines offer another advantage: they offer a lot of strength and rigidity to the hull.
The chine itself is called a "chine log" and is one of the structural stringers that run the length of a craft. This stringer is the turn of the bilge and is set into the frames so that the planks can lay flush against it.
This stringer really stiffens up the frames of a wooden boat and transmits considerable amounts of load amongst the frames in the area on that side of the hull. Since the frames work more in unison, the frames can actually be spaced further apart and be made considerably smaller than if the hull had soft chines.
Less weight in frames translates into less weight overall. This is yet another reason hard chines are favored on powerboats where speed is the priority and keeping weight down is imperative.
Hard chines also make initial construction and later repairs much simpler. On a hard chine vessel, there are very few curves and the curves that are present tend to be very subtle. This means that the planks follow relatively straight paths and require very little twisting or bending to get into place. Not having to custom contour each plank means that fabrication can proceed much quicker. If you have to replace a rotten strake, fitting the new plank will also be a much easier endeavor, as it will pretty much be a straight strake that runs its length in a flat manner.
The simplicity in construction is all thanks to the chine. The topsides run down straight and meet the chine log where they end. The bottom planks run from the garboard up to the chine where they also end. There is no rounded section that needs to be fitted with scrubbed planks and corners to fair off as you try to blend a curvature into the turn of the bilge. The planks run along until they get to the corner where they simply stop and start again in a new direction without any effort on the part of the builder.
Ease of construction, ease of repair, and greater stability all make hard chine boats desirable powerboats and dinghies for your sailboats.