... this is completely hypothetical) while Michigan has great connections to the ... going there as going to Michigan or Cornell in this hypothetical ...
Thanks. Yeah, good point. I'm going to try to avoid writing one. This would mainly be for Michigan, which asks for an explanation if there's a difference of six or more points.
I think you should be weary when admissions say optional. When they say "optional", I don't think it usually is. I'd say write it unless you really can't think of anything and what you're writing sounds forced and insincere.
One really strong optional is better than one really strong optional plus one mediocre optional. If only one of the optional prompts speaks to you, only write that one.