A good sense of humour isn't just a way to make your workday more pleasurable, it can also help you perform better (and get ahead). Forbes notes that a playful atmosphere can be incredibly conducive for ideation in creative fields: it helps turn off that part of your brain that monitors your own behaviour and feel self-conscious.
And even if you don't work in a field that's considered "creative", humour could go a long way towards furthering your own personal success:
A Robert Half International survey, for instance, found that 91% of executives believe a sense of humour is important for career advancement; while 84% feel that people with a good sense of humour do a better job. Another study by Bell Leadership Institute found that the two most desirable traits in leaders were a strong work ethic and a good sense of humour.
Of course, being the office clown is easy to take too far, and work isn't the place for comedy that pushes boundaries. If you're not funny, that's fine too -- but if you've got it, use it. Hit the link for a full list of ways work and funny can mix together well.