Not the greatest picture, but here's my 38T ring on a 105 (6-speed era) crank. You can see a smudgy spot where the chain is able to contact the tab on the crank spider.



My mental image is that of the chain not being able to settle completely at these spots, so it's a little more likely to get pulled out of position when under tension. One wouldn't compromise the integrity of the crank by Dremeling off a tiny bit of material at these contact points, methinks.