It can take some of the emotional sting out of it by seeing it in writing or finding the words to express what you feel.
It can help get it into perspective. Sometimes just writing it down can help you feel that maybe it's not that bad.
If you're dealing with a problem, getting it all out of your head can then leave space for the subconscious to get to work and come up with a solution.
If you are having a communication problem with someone - work, family or partner. Write down what you feel. What is it that you would like to say to them?Give it a try. Get a notebook or journal and each morning or in a quiet time, just start to write. Don't worry about spelling, neatness, grammar - just write as it comes.
There is a book by Julia Cameron called The Artists Way and in it she describes something called the Morning Pages. You write these every morning, as soon as you get up - before you do anything else. Write three pages of whatever comes to mind. It literally is a brain dump or a 'stream of consciousness'. Anything goes and it doesn't matter what you're writing as no-one is going to read it and you don't read it once it's done - at least not for a while. The interesting stuff comes afterwards once you've unblocked your creativity.