This totally depends on your community. For us the avatars on the index page are just clown vomit.
The reason is that 99% of the topics on our would have the maximum number of avatars shown. This produces a wide and colorful column to the middle of the screen, which has too much weight against a natural white background, and adds very little information as all topics are popular - everybody jumps to every topic. Very different to the user behavior that we see for example here.
One way to look at it is the topics/posts ratio. Here at Meta there are 160 new topics and 2.8k posts for the last 7 days. On our community there are only 22 topics but 4.1k posts for the same period.
The avatars do work on small and growing communities, as it makes the front page look busy / active.