The pros of using World War I aircraft were that they were very helpful in reconnaissance. They could fly over enemy lines and see the enemy's troop movements, and, after they were eventually armed with machine guns, they could provide an offensive advantage.
The cons of using these planes were that they were very dangerous, and the average British pilot had a life expectancy of about 70 hours when flying above the Western Front (see Lawson and Lawson, cited below). The aircraft were too cramped to carry parachutes. In addition, it was very time consuming and difficult to construct planes during this era. A typical two-seat plane had more than 50,000 different parts and took 4,000 hours of labor to put together (see the Red Stone Rocket link below). Some planes of this era cost about $7,000 to build (at a time when the Model-T cost $400), so they were also very cost prohibitive.
Eric Lawson, Jane Lawson. The First Air Campaign: August 1914-November 1918 (Da Capo Press, 2002).