Let Wikipedia speak.
Advantages
A dry sump offers many advantages. The most obvious are increased oil capacity afforded by the remote reservoir, and the capability to mount the engine lower in the vehicle because of the lower sump profile—lowering the overall center of gravity. The external reservoir can also be relocated to another part of the car to improve weight distribution. Increased oil capacity by using a larger external reservoir than would be practical in a wet-sump system cools the oil more and releases entrained gasses from ring blow-by and the action of the crankshaft. Furthermore, dry-sump designs are not susceptible to the oil movement problems from high cornering forces that wet sump systems can suffer. In a wet sump, the force of the vehicle cornering can force the oil to one side of the oil pan, possibly uncovering the oil pump pickup tube and causing a loss of oil pressure.
Because scavenge pumps are typically mounted at the lowest point on the engine, the oil flows into the pump intake by gravity rather than having to be lifted up into the intake of the pump as in a wet sump. Also, the scavenge pumps can be of a design that is more tolerant of entrained gasses than the typical pressure pump, which can lose suction if too much air mixes into the oil. Since the pressure pump is typically lower than the external oil tank, it always has a positive pressure on its suction regardless of cornering forces. Another phenomenon that occurs in high-performance car engines is oil frothing up inside the crank-case due to the very high revs agitating the oil. Lastly, having the pumps external to the engine makes them easier to maintain or replace.