The purpose is to attack ground units with bombs, dive bombing is the most accurate way to put your bomb on target.

From 10,000 to 15,000 feet, put your plane in a dive toward the target. You should be at an angle between 45 and 70 degrees, be carefull not to dive too steeply. As you pick up airspeed, make gentle turns to stay on target, and throttle back if you have to, to avoid excessive speed; at around 3,000 feet.
Because you are not diving straight down, you may need to compensate by aiming slightly behind the target.
Once you release the bomb, pull back on the stick gently to pull out of your dive, and ease off the throttle if your airspeed is high. Be carefull, if you pull back too hard too quickly, you may stall or damage your airplane!. After you pull out if the dive, add power and level out or climb away from the target.
Don't get careless checking to see if your bomb hit, enemy fighters or flack could catch you in this vulnerable moment.

Drawbacks:
Fighters can carry bombs, but performance is hampered by the additional weight.
While on the crucial bomb run, you are vulnerable to ground fire, and you are an easy target to hit.