What the balancer is actually currently doing can be opaque. In times when the shards are out of balance and do not appear to be balancing, and where there is no good indication in the logs indicating an issue with the balancer, it would be useful to have some way of querying what the balancer is actually doing.
The locks collection does not give you enough information, as you can only reliably tell if the balancer is on or not, or if it is currently in a balancing round. You can't tell if the balancer is currently calculating, or moving a chunk or not able to move chunks for some reason that is not an error. In either case, having more insight into what the balancer is currently doing would help diagnose issues.
If there is a location or object to store state of the balancer this could make it available to be queried from the shell or drivers, given that additional logging may not be the solution