Column size adjustments is based on the recommended column size for current Pega version to which you are upgrading too.
The Upgrade Applications Schema utility only adds missing columns or missing indexes, and adjusts column sizes. The Upgrade Applications Schema utility does not make any other changes to your cloned tables. You can either apply the changes automatically, or review the changes first.
This step can be carried out automatically or skipped during the actual upgrade and can be performed at a later point as well from the designer studio.