My worry was trying to get the chainline smack in the middle of the cassette. That way, I could use the entire range of gears without too much deflection either way. I would choose my crank size based on that. Still though, I've often not been paying attention (usually toward the end of a long ride when I am somewhat spent) on my "normal" 2x10 setup and I've caught myself on the small front ring on the next to last (smallest) cog on the cassette. How is that any different than a 1x10 with chainline in the middle pushed to either extreme?