The long street starts at the Municipal Complex downtown, and ends at The Plaza de Armas. It was very close to our hotel, so we had occasion to walk down it, and drive down it several times during our stay in Cuzco.
We found it to be a very busy street filled with Money Exchange Stores, Hair Cutting Stores, Souvenir Stores plus plenty of Restaurants. We felt safe walking up and down, even late in the evening. People seemed very nice and helpful.
Since it is such a busy thoroughfare, everybody gets to see it at least once while staying in this city.