Language Documentation, the scientific description of minority languages, like the delineation of any species of plant or animal, contributes foundational knowledge about our world, and in this case is critical for ongoing research in language, culture, behavior, cognition, and so forth.
It also assists the people themselves in developing their dictionary, pedagogical grammar, primer, reading materials, providing what is a basic (linguistic) right—to read, write, and articulate their own thoughts, as well as the thinking of others, and to join the national and international conversation.
Here are some helpful links:
What is language documentation (a book to purchase providing good details)
WALS (The World Atlas of Language Structures, online version)
LD&C (an open journal of Language Documentation and Conservation issues)
Here are some links to descriptive journals of interest to me in my area of the world:
JSEALS (open Journal of the Southeast Asian Linguistics Society)
LTBA (subscription journal Linguistics of the Tibeto-Burman Area)
MKS (subscription journal Mon Khmer Studies)
NEILS (open journal North East Indian Linguistics Society)