'Generally, I received the same wangs (empowerments) from Dudjom Rinpoche maybe hundreds of times. One of the benefits of receiving a wang is to purify samaya. When we receive a wang, afterwards do we keep pure samaya?
Each time we receive a wang we pacify broken samaya, increase its power and refresh its blessings. It is always beneficial to receive a wang. When there's something important, we do repeat wangs. For example, when people are very ill, they'll repeat a long life wang a hundred times. When people are dying we do a Zhitro (hundred deities) wang a hundred times. It's only beneficial and can never hurt to receive empowerment.'
Lama Tharchin
http://www.vajrayana.org/pommo/user/mai ... ail_id=448

