Upgrading firmware makes sense as new firmware versions normally have optimizations, added functionality and also possible bug fixes. In some cases new firmware is also necessary to support new/upgraded hardware parts found new hardware revisions.
However, downgrading sometimes makes sense as well. For instance, when running a custom application which is build at a time in the past based on a specific firmware version. We have seen that newer firmware renders the older application unusable. Therefore by default we always try to have the same combination of firmware level and custom application installed to make sure all is compatible.
Both these insights on upgrading and downgrading firmware leads to the fact that you always have to proceed with caution.
This way you can always revert the attempt to the old situation in case things go wrong.