What are the benefits for using "mapping" in ElasticSearch?

Assuming that I only have one type for a given index, what are the benefits for defining a "mapping" for it? One reason I can think of is that the mapping makes it easier to access a user-defined type in the search result. On the other hand, if I have a data structure change, I would have to repopulate the mapping and reindex the data, which can problematic in production.