Are there benefits to keeping a dream diary?

Making a habit of recording your dreams immediately upon waking is supposed to help you start to remember them better and more frequently, as well as aid in learning how to lucid dream. I have a friend who successfully taught himself lucid dreaming.
When do you actually write in it? You should keep it beside the bed and grab it before you even sit up. I don’t keep one anymore but I’ve tried a few times and would often reach out blindly and start scribbling in it with my eyes still closed. Then later I would try to make out what the heck I wrote and re-write it with more detail, if I remembered any.

Besides the two reasons above, it’s really interesting to go back and read dreams from years before. Especially when it triggers a super vivid memory of them. :)

what @codette said plus it helps jog your memory – often while writing down a dream I suddenly remember other dreams, as in I remember 2–3 other dreams at once and start writing them all down one by one, it’s amazing how much you remember and some dreams are just worth coming back to. Bonus: if you’re a writer some of those dreams may very well inspire you to write something.

(I mean, seriously, some of my dreams are freaking Hollywood-production material, lol)

The only reason for me would be to humor myself at a later date of all the weird stuff I dream up! considering there is no science that can prove what dreams mean, I’m not sure practically what you would get from it.

Dreams are your subconscious mind’s way of interpreting situations. If you keep a dream diary you can begin to understand your personal responses (every dreamer has personal images that are unique to themselves). As you record your dreams, you will come to know if you are neglecting yourself / your interests. You will begin to know the why of something that makes you uncomfortable. It will give you a clearer vision of the world around you. I have been keeping a dream diary for a very long time.

I’m glad you posted this question. I’m inspired to try it again.

Dreams are an excellent source of creative material for artistic endeavors. Almost all of my novels, stories, and a few of my paintings originated from dreams I recorded in my dream journal.

I used to record my dreams a lot.
A DIY self-hypnosis tape can help you to wake when a dream is over and to recall all the important parts long enough to write it down, and to get back to sleep. Practice writing in the dark without opening your eyes, use your non-writing hand to mark the level of the line you’re writing and give yourself plenty of room for the next line.

Jungian dream interpretation holds that the people and things in dreams are a lexicon related to the feelings they hold for you. They tell a story that the psyche needs to express to reconcile what happened in waking hours. There are some ‘archetypes’ that seem to hold true for most people, but mostly each of us has our own dream language.
What you learn from your dreams depends on all kinds of things, including feelings you didn’t know you have.