I wouldn't say I'm having issues with traction, I've got lots, just always nice to have more cornering ability and stopping power.
One reason I'm looking at 235/40 is the older JDM sti's ran 205/50/16 from factory so I'm trying to stay closer to OEM size. Also, if I get a wider tire, I might be able to get one that last a little longer than my star specs and provides about the same amount of grip due to the extra surface area.