The tire numbers are width- height RATIO and rim size.
So the 200/60/16 is a little wider and a little shorter than the 180/70/16.
I say "a little shorter" because the height of the 200/60 is 120 mm tall and the 180/70 is 126 mm tall.
Personally, I think it's mostly a LOOKS thing. On heavier vehicles, it's a capacity thing. For instance, on my boat trailer, the 180 supports 1740 lbs while the 205 supports 1860 lbs at 50psi. And because my boat and gear weighs in close to 3300 lbs, I need two 1860lbs tires to keep rolling down the freeway. I learned this the hard way with a tire blowing out on me on a trip...... the third time.... sheesh. slow learner.