The first time I tried 165's on my road bike (I'm 5-10) my first reaction was not great. "I'm riding a little kid's bike!" is how it felt. But I got used to them and I found it was a lot less work to get the pedals around than with 175's. Slightly less leverage, as the person above noted, but overall, less tiring on the body, and less taxing on the knees and hips.

Shorter cranks tend to make me want to spin more. But 175's always gave me knee, hip, and lower back pain. Nothing that didn't heal up eventually, but why deal with it if you don't have to? Glad I ditched those. 172.5's are OK for short rides, but I mostly prefer 165's and 170's these days.