Your factory bump stops do a great job keeping your tires from rubbing against your fender flares, as well as making sure your shocks do not over compress or bottom out during extreme travel. However, factory bump stops are made of rubber and can degrade over time thanks to road debris, chemicals and oils.
When it is time to change, many choose to upgrade to polyurethane bump stops as these are stronger and not affected by things like oils, chemicals and the like. Others look to heavier duty mechanical, or hydraulic kits which limit compression and provide a smoother ride. Also, bump stop extensions are a popular choice for the off roader who has added a suspension life and larger tires, as these help add strength and extra clearance for tire travel.