There’s nothing more dangerous than an average manager with free time on his hands. When your work is solely coordinating and assigning other people’s tasks, topping off a slow day usually means making up more (needless) stuff for others to do.
This is in part the tyranny of the 8-hour work day paradigm. When the work is progressing as planned and the core issues have been addressed, the right move for the manager is often to step back. But if all you know how do is “manage”, there’s no fallback. Nothing else to fill your time with.
What you’re left with is net-negative management. That the presence of a manager actually detracts more value than not having one at all would do.
The alternative for many smaller teams or shops is the combined idea of managers of one and working managers. That management can be less than a full-time role, it can be a responsibility that people who also does the work can take upon them when needed.