Time Machine will (eventually) use all that you give it. At that point, it will start deleting the oldest back ups. With a large enough drive/partition, that could be several years. With a much smaller drive/partition, it may never exceed several months. Size is determined by your history needs.Lastly, don't forget other backups you might have in the 'cloud.' iCloud is but one place. Dropbox and similar free services are also available. Then, there are paid services like CrashPlan, etc.
SupeDuper backups tend to grow rather slowly, depending on the type you have chosen. It will basically be the minimum size of whatever you have selected for backing up. The maximum would be the entire internal drive. That becomes the base line for the size. It will only grow when you add new files/apps or when current files/apps grow in size. Size of the partition depends on how actively you add files/apps or increase their sizes. I'd say a very rough minimum partition size would be twice as large as your current used space on the internal drive. You really need to read the manual for a more detailed description of how SD works with its various methods. Simply not backing up many items that can easily be replaced by re-downloading or with Recovery Disks will help keep the minimum size down considerably.
I think they have a show about <that kind person> on <TV>...![]()
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Or not To complete a backup...WAIT!indeed, whether 'tis nobler...