The map function has been created to only emit a key/value pair, and your should try to keep it as small as possible.
This is why you see most of the application emitting only a key and nothing else. This is just because the index is on disk and called using a REST API, where in Couchbase when you get the document with a cb.get() operation you use the fast and scalable memcached protocol.
So the good patter is to:
emit the key in the map function
do not emit value if you do not need it in a reduce function, you can emit also as value one attribute or an aggregate
query this index (view) with or without parameters
this return a list of document id, use this list to get the document using cb.get() operation, that are using memcached protocol and will cache the document automatically.