How do we as HRM professionals objectively determine the “value” of on-the-job-trainings?

The most common type of training at all levels of an organization is on-the-job training which happens innately. Whether the training is planned or not, people tend to learn from their job experiences. Based on your experiences, discuss the added value of on-the-job training. How do we as HRM professionals objectively determine the “value” of on-the-job-trainings? Then, discuss the problems of on-the-job-training that should be taken into consideration. Finally, make a recommendation as to how on-the-job training can be assessed and used for succession planning