This is some information I got after searching the web:

There are three types of tears only one of which is associated with crying. One type, known as basal tears, continuously lubricate our eyeballs while another, reflex tears, are produced when our eyes become irritated, as when we chop onions. The third type are generally referred to as emotional tears and are what are produced when we cry as part of our response to a range of psychological triggers. Such crying tears not only have a different cause but also have a different concentration of chemicals, hormones and proteins to both basal and reflex tears.

During stress (strong emotions or pain) our bodies produce increased amounts of brain signal proteins and extra stress hormones. Tears produced under these conditions contain some of these proteins and hormones. They get rid of some of the components associated with our discomfort. This may be why so many people feel so much better after a good cry.

While it may not be something you want to do often, a good cry might be beneficial on occasion.

I hope this answers your question.