Offline License Life parameter can be found on SKUs page. This parameter is only valid for semi-online and offline activations and can be applied to Perpetual licenses only.
It limits the license's validity time. For example, if you set 90 days to Offline License Life parameter for an SKU, the license file will be valid for the next 90 days after the file is downloaded. It has to be downloaded at least every 90 days to use the license.
If you have a refund policy or something like you need to cut the license validity, you might want to use this setting.