As noted in RHODS-3335, changing the default PVC size involves a brief outage of JupyterHub launcher; administrators should be aware of this before they make changes. Per Luca's comments:

JH is redeployed every time the PVC size is changed (this is to pick up the actual change from the configmap)
If a user already has a bound PVC before the default is changed, their PVC will be unaffected by the change and keep the original size

If a user is already using a notebook (i.e. their server is already spawned and running) they won't notice anything.
Other users might be impacted while trying to access the JH spawner page or trying to spawn a server, since the rollout will make JH unreachable for ~20-30 seconds, possibly resulting in https://issues.redhat.com/browse/RHODS-3180 or similar.
However I don't expect this setting to be changed frequently and/or during the org's working hours? This seems like an action that an admin would take while setting up RHODS and possibly never change again