When new members of the NSA ( National Speakers Association ) ask my friend Randy Larsen if their speeches should be humorous, his answer is "only if you want to get paid."
At the 2017 world Toastmasters Convention, the Toastmasters president got solid laughs when he lost his place, fumbled with his notes and said " UH - OH. My wife is going to bring this up in her evaluation." This was at the keynote no less.
Humor in speeches is important for many not so obvious reasons. I submit that it is not possible, but necessary to make serious points with humor. Adding a humorous twist keeps the audience engaged and makes the content easier to recall. I constantly have to get across technical concepts to people from varied demographics. Humor avoids " MEGO " ( my eyes glaze over ) every time it's tried.
Self deprecating humor is a force multiplier. It's humbling. The audience won't feel like they are being lectured to ( It's an ancient cliche, but any seasoned actor will tell you the audience won't remember most of the lines, but they will remember how they players made them feel. ). Personally, I feel relaxed with my primary physician who admits he should do better with leading by example. He drinks too much, doesn't exercise and indulges in junk food away from home. My wife's best friend is a therapist. She vents to my wife about how her teenage kids are driving her nuts.
I'm no professional speaker, but this tactic works especially well on me probably because I enjoy irony. A professional psychologist could maybe explain why self-deprecating humor works so well. Maybe it has something to do with schadenfreude.