Training new climbers and groundsman can be difficult and costly, but it is an essential part of running a thriving tree service. For the more experience arborists, I'm sure you can remember your first days on the job and how terrifying it can be with so many life threatening hazards around at all times. Looking back its obvious that the visible hazards were only the beginning as the more time you spend doing tree work the more hazards become visible.
Poorly trained employees are likely to get injured. They break more equipment, dull the chainsaw teeth more quickly, and cause more damage to clients property than well trained employees. This seems obvious, but these are the inevitable costs associated with NOT training the crew. Thankfully training can happen on the job, and doesn't need to be a separate expense. Often, the best training I have both given and received has been as a result of a slower pace on the job and someone willing to point out to me things that I need to know. This can be done by any of the more experienced employees, and should be encouraged.
Training a climber presents a particular challenge because of the inevitable distance between a teacher on the ground and the climber in the tree. Helmet communication systems such as the ones produced by Sena and Packtalk can be indespensible for this purpose. The Cardo Packtalk Bold system has excellent noise cancellation and can allow for clear communication across the job-site. This is one piece of safety equipment that has proven to be worth its weight in gold.