This alert is based on an extrapolation of the space used in a file system. It fires if both the current usage is above a certain threshold and the extrapolation predicts to run out of space in a certain time. This is a warning-level alert if that time is less than 24h. It's a critical alert if that time is less than 4h.
A filesystem running completely full is obviously very bad for any process in need to write to the filesystem. But even before a filesystem runs completely full, performance is usually degrading.
Study the recent trends of filesystem usage on a dashboard. Sometimes a periodic pattern of writing and cleaning up can trick the linear prediction into a false alert.
Use the usual OS tools to investigate what directories are the worst and/or recent offenders.
Is this some irregular condition, e.g. a process fails to clean up behind itself, or is this organic growth?
<Insert site specific measures, for example to grow a persistent volume.>