If somebody wrote a story about a space trucker who becomes a vampire on the long haul to Ganymede—not a real example, but one anybody's free to use—because it had deep biographical connection to them, then yes, that's something I'd want in a cover letter. But not if it's just describing the plot. 😀
Lev MirovWhen "please disclose if this story is based on your identity or life experience in any way you think we should consider" started to become relatively common, I saw a lot of cover letters with the synopsis sentence about "this story about X is based on my Y" appear, and even use it sometimes myself.