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.
Several updates are available for the standard usage reports in the Microsoft 365 Admin Center. One helps Office 365 tenants understand the changed user activity profile due to remote working. Another gives views of user activity across the complete tenant. The updates are useful and interesting, but an ISV product will do a better job of analyzing and reporting the same data.