An item in the Teams release notes tells us that analytics are now available for channels. You can find out how many topics and replies are posted within a channel. You’ll probably know what channels are in heavy use anyway, but seeing how little traffic some channels get is a good way of knowing that maybe your teams don’t need those channels.
The Teams desktop and browser clients now boasts the ability to report per-team and cross-team analytics. The information is interesting (at least the first time you look at it), but some doubts remain about its accuracy when the different methods of reporting are checked against each other. I’m sure it’s nothing more than timing, synchronization, or something else getting in the way.