For my normal EDC, I carry 7+1 in my XDs9. No spares. Most daily situations, if anything happened that required me to engage, it would be a personal situation (i.e. me working in real estate that I own, solo) and I would hope that my practice regimen would have me on target within 8 shots.
I also own a live audio company (sound for live bands - fairs, nightclubs, parties, etc) and when I have an event, I do tend to carry a spare 8 on my belt in addition to the 7+1.
My overall thought process behind that is, I'm not a LEO and am not "obligated" to step in, regardless of personal threat. That said (and I hope I, or anyone here, never have to put any of this into practice), I like to think that I would evaluate the situation and decide quickly if one mag would solve things, or if the threat is too great and I'm better off not engaging, or exiting.
A PERSONAL threat? One mag should do the trick due to proximity.
A threat to one of my shows / one of my crowds / one of my bands? That's a tough call. I have sheepdog in me and I take my shows personally, and I would likely engage a single offender because, as "the guy" running the show and running the room, I tend to locate myself in a position with good overview of the entire room and crowd just so I can do my job - the tactical advantage is a side-effect. But a group of offenders? I don't know. It would depend on THAT situation, in THAT room, with THAT crowd and THAT offender(s).
All that said, I am VERY MUCH looking forward to the state of Maryland approving the Hellcat for sale (or winning one here!). I'm not one to have a lot of "stuff" hanging off my belt (mainly due to wardrobe and not wanting to freak out all the anti-gun folks, but also due to bend/twist/lift/stretch activities that I encounter every time I do a show), but I do like the idea of having the larger capacity within the firearm. Just in case.