The original purpose was to have a place for the 蹲（つくばい）, because in the old days tea rooms where connected to the house and guests would enter from there.
小堀遠州（こぼり えんしゅう）said:
Eine Gruppe Sommerbäume
Ein Streifen Meer
Ein blasser Abendmond
The 蹲踞（つくばい）is in the inner 路地, and filled in front of the guests.