I've slipped in a couple of TUNES I made up, after I'd tested them on unsuspecting music buddies and gotten approval, but never sung anything I wrote. I don't write many songs with words. My best one is much too long for most performances (eleven verses); it's a good song and doesn't sound conspicuously "wrote", nor is it personal, but most audiences just don't want to sit through something like that.

I'm perfectly aware that I don't have any talent for "singing my diary" so I, personally, would never subject an audience to something like that (I'd probably never even write something like that--I tend to write ballads that have nothing to do with my personal life), but if you're good at it, what the heck.