There is a special religious significance assigned to sky burial by
Tibetans. A sky burial is seen as being a final act of
compassion carried out by the dead. Being 'buried' in this fashion provides nourishment to other living beings, a theme seen several times in story of the earlier lives of the
Buddha in the
Jataka Tales, particularly in the story of
King Shibi. It is seen as an act of self-sacrifice for the benefit of others- even though the primary actor is already
dead.
Additionally, Buddhists view attachment to the body as one of the more thorny desires to be rid of. Agreeing to have one's body disposed of in this manner is seen to embody a commitment to be rid of this attachment. It is therefore seen to bring merit to the deceased.
In some cases, a close relative is asked to preside over the ceremony (most Tibetans have (or would have had, prior to the Chinese invasion) at least one relative who is a monk). Viewing a sky burial is also said to be instructive- it teaches detachment, and fosters an awareness of mortality and impermanance. At the same time, a sky burial is considered a very private and sacred event; the curious should be warned that if you attempt to attend a burial without a personal invitation from the family of the deceased, you will almost certainly be chased off by rock-slinging mourners.
The sky burial practice, in many ways, is not far from other Buddhist death-related practices, such as the printing and distribution of Dhamma-related books or pamphlets at a funeral (done in Thailand, especially at the funerals of monks or meditation teachers), or the recitation of scriptures in the name of the deceased (done in several East Asian nations, including Japan, as well as in Theravada countries such as Thailand and Burma.