This question already has an answer here:
When breathing out during swimming, I've come across conflicting info - a swim instructor years ago told me to "exhale it all out immediately", so after I take in my breath, once my head is submerged, I breath out fully.
I prefer, and the youtube videos I just watched support this, exhaling over time. So I'll breath in, and then once my head is submerged I'll breath out for the duration, until I turn my head to take another breath.
Is one way "better" or more efficient than the other? Is there debate between the two methods? Is one way "just wrong"?
Note linked question doesn't deal with breathing out, this is a different question.