At Nicola Griffith's blog, a study finding that putting your feelings into words activates the same areas of the brain as emotional self-control. Although given what I've recently read about the dubious value of interpreting fMRI (basically, some scientists are finding correlations because they're throwing out a lot of data) it's hard for me to evaluate this finding.
But just for the sake of argument, let's pretend it's true. It does kind of make sense: you have to discipline yourself to put feelings into words rather than acting them out, so you're practicing controlling your feelings already.
And parents of toddlers everywhere are vindicated in saying "Use your words, dear."