Voting comments does help a lot with engagement, for sure. I think that it's also helpful for new users to grow on the platform. Its not easy to grow organically on the platform when you first start out, especially if you are only relying on rewards from a post. Just my opinion here but a person should only post once per day or maybe twice if you really have a lot to say so growing by posting alone is severely limited. Commenting on the other hand, a person can make as many of those as they like, provided they aren't spammy and pass people off lol. Votes on comments are kind of like a faucet effect for new users. Small trickles here and there really add up over time and help with organic growth. The incentive to comment also builds relationships over time as well which also leads to growth. Overall, voting for comments is a good thing in my opinion