Process changes can come two primary ways: top-down direction on how things need to be done going forward or people on the ground deciding to do things better.
In the top-down bucket, changes may be driven by new technology, new reporting requirements or just a new way of thinking about things. Usually, these are accompanied by some level of controls to ensure the changes stick and are followed. The control may be as simple as a standing meeting with a standing agenda item. It may come in more strict forms of reviewing log-ins and update timestamps. Top-down ensures the new rules are followed (regardless of whether they are better or worse).
Guerrilla improvements usually are driven by need or laziness (not always a bad quality in employees). These changes happen because someone sees or experiences something that could be fixed. Maybe the solution lasts only as long as that person remains in the role, maybe it dies after a week because there is no support for it, maybe it becomes a core part of the business. The difference in lasting comes in part from an organization’s culture and desire to promote the new.
Both types can lead to real improvement or new-found inefficiency. Both could impact just a single individual or spread company-wide. Toyota decided long ago with their Toyota Production System that improvement could come from anywhere and was worth pushing both bottom-up and top-down as it is found.
There are still many cultures and managers out there scared of the new and willing to put down bottom-up change suggestions. The best managers will still be those that promote good ideas regardless of where they come from and work to improve poor ideas.