if you don't use leases, then it's up to someone to manually delete items or have a different tool to track their lifespan.
Thinking out loud ... If users leave vapps powered off for a long time to clone or copy them ... isn't that was a catalog vApp would be for? this way it doesn't count towards their personal quota and leases.
you could use the catalog as a method of 'long term storage', then have deployment and storage leases for the short term.
