When you don't tick "Maintain field size", you can tick this option.
When you tick "Force resize", then all the changed fields (outside of list boxes) will change their width, according to the new picture, no matter if they had a default width or a fixed one, for this particular procedure.
See Force resize for further explanations.
This option will be activated only if you tick the "Override Global" setting. The value specified here will take effect instead of the global value.