When consumers only see  prices once they visit stores, and some consumers have time to comparison shop, co-location commits stores to compete and lower prices, which draws consumers away from isolated stores. Profits of co-located firms are a single-peaked function of the number of  shoppers---co-located firms thrive when there are some shoppers, but not too many. When consumers know in advance whether they  have time to shop,  effects are enhanced:  co-located stores may draw enough shoppers to drive the expected price paid by a non-shopper  below that paid when consumers do not know if they will have time to shop.