Going cross country with stiles, stairs, and other fence or stream crossing situations
where you have to portage the bike then get back on and ride to the next occasion .

where you carry the bike a while,then it carries you, then you carry it, and Etc.

maybe..

Other than that , bring one for sightseeing Off the bike,
space to pack fresh produce at last food stop, before camp.
maybe use it as a stuff sack on top of the rear rack on the road..