We trained them a lot in kenpo, as part of our self defense techniques, but didn't use them much in sparring. I do train them frequently on the heavy bag. They can also be useful from medium distance, as Urijah Faber showed against Mike Brown in their second WEC fight. Jon Jones in the UFC is also very good with elbows, particularly spinning ones.
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"In case you ever wondered what it's like to be knocked out, it's like waking up from a nightmare only to discover it wasn't a dream." -Forrest Griffin