...
Depending on the chosen format type, a number of different parameters will appear. Most parameters should be self-explanatory. However, a short description of some of the key features can be found here.
Generation
Renditions of assets can be either generated on-demand or pre-generated.
...
Custom renditions are always generated on-demand. However, if the exact requested rendition has already been generated, it is reused. Custom renditions are automatically cleaned up if they have not been downloaded in a while. By default, custom renditions are cleaned up after 30 days. This can be configured from the general settings page in the Media Manager. Only custom renditions are cleaned up.
...
Deletion
It is possible to manually trigger the deletion of renditions. This can be done via the automation step “Delete asset renditions”. Note that the automation step only deletes a rendition if it is available. Consequently, renditions that are in the process of being generated are not deleted.