They encourage the players to use teamwork and find out different ways to kill the special infected.
Going anywhere by yourself because you will probably get killed.
Hunters: They are made for downing single or strayed survivors.
Smokers: They are made for pulling people off high places for a huge health decrease or insta kill.
Boomers: They are made for when you are low on health and cause a wave of zombies to kill you.
Jockey: They are made for riding survivors off edges and running away and doing it again after they heal.
Chargers: They are made for plowing a whole team off a ledge that causes insta kill.
Spitters: They are made for helping other special infected to cause massive damage.
Tank(Extra): They are made for going after the weaker survivors because they can keep up and will do massive damage. They can do a special move that requires both triggers to be hit at the same time its called the hay maker. Basically they will smash the ground and at the same time will pick up a rock and throw it at the survivors.