Shopify POS is the in-store side of Shopify. Stores, pop ups and the online store all read from the same products, inventory, customer profiles and orders, so there is no overnight sync to go wrong. For brands already on Shopify Plus it is usually the shortest path to retail and online that agree with each other.
Most of the value is in the setup. We plan stock locations, staff roles and permissions, and the omnichannel flows customers now expect, such as buying online and picking up in store, returning at any location, and ordering an item the store has run out of for delivery. Then we connect it to the ERP or inventory system that holds the real stock count.
When stores and the website already run on separate systems, we look at moving retail onto Shopify POS as part of a wider omnichannel and POS project, so customer history and stock stop living in two places.