It is sunnah if you are praying alone or as an imam, to have a barrier (sutrah) in front of you that will prevent people from walking in front of you, and to enable you to focus properly on the actions of the prayer.
The Prophet salallahu ‘alayhi wa sallam said: When one of you prays, let him pray facing a sutrah and let him draw close to it and not let anyone pass in front of him. And: Let one of you use a sutrah when praying, even if it is an arrow.
According to scholarly consensus, in the case of one who is praying behind an imam, it is not recommended for him to use a sutrah , because the sutrah of the imam is the sutrah of the one who is praying behind him, or because the imam is a sutrah for him. [al-Mawsoo‘ah al-Fiqhiyyah (24/177)]