Hello,
You can configure the time that the client has to keep the files within cache folder, either setups, exe, iso, bat... files, freeing this ways space in your clients.
After Altiris removes those files, you will keep the folder structure, logs etc but not the packages. If the client requires the files again for any reason (maybe the software has been uninstalled and the policy install it again), the files are downloaded again.
I'm not in front of the console because is late, but is not difficult find out where this is configured.
Hopefully it helps.