Smaller driveline parts like U-Joints and Yoke kits can be the first to go the more the vehicle is driven - especially if the ride involves a lot of off road activities. So if you are getting excessive driveline vibration, it may be time for a change.
Replacing those failing U-Joints will retain the flexibility your front and rear driveshafts need so they do not become over-stressed and break. Some even prefer to swap out the still-capable factory U-Joints for a heavier duty one that will absorb all off-road punishment. This can be a must should the vehicle have a suspension lift added. In addition, changing out the pinion yoke will help alleviate seal damage and fluid leaks. Many times, a Slip Yoke Eliminator (SYE) kit is recommended for suspension-lifted vehicles.