Static resources are delivered with an URL that is unique within each releases. This makes sure that when an update is installed, all static resources are reloaded by the browser and no browser cached version is used. This is necessary because in practice it is not possible to force browsers to not use a cached version.
The problem is that when a system layout is being modified in between a new release and e.g. new images are added to the theme, the browser will still show the old images because of browser side caching. To force browsers to reload the theme, the theme URL must be changed.
This issue offers a button to add some junk to the URL so browsers are forced to load all static resources again. The junk (actually an integer) is only held in RAM. Once the server is reloaded, the URL returns back to the original value. But this is not a problem as there is no need to restart OpenOLAT unless a new release is installed