Comprehension-based learning and the Roles of Output in language learning (Peter Skehan)

Roles of Output in language learning

1. To generate better input: good output serves as good input.
2. To force syntactic processing: awareness of need to produce speech makes better listeners of the means by which meaning is communicated. Syntax, etc. It causes input and listening to be used more effectively for interlanguage development.
3. To test hypotheses: speaker can control the agenda, take risks, look for feedback on the points of doubt in his/her developing grammar. This makes learning more efficient, because speaker can build upon the feedback.
4. To develop automaticity: real time speaking needs speed in processing. Linking utterances automatically reduces/saves processing time and spares the same for planning responses in speaking. Fluency comes by practice. (In languages where morphology (word order, etc.) plays a vital role, speaking helps faster learning.)
5. To develop discourse skills: to be an effective communicator, it is not enough to have sentence construction skills. Participation in discourse is the only means by which these skills can be achieved. 
6. To develop a personal voice: One needs to steer conversations along the interests of the speaker, finding ways of expression to mean what one wants to mean.

Importance of output
The points above detail the inadequacy of simple listening for language learning.

But is output sufficient as an efficient language learning tool?

Skehan says that the points above indicate that output is an efficient agent in learning language. Output has a central role in promoting interlanguage development by forcing syntactic processing, testing hypotheses, and developing automaticity. These stand for fluency and form.