IT can realize significant per-site cost savings by eliminating the WAN, including reductions in or elimination of connectivity service costs, hardware costs and licensing costs for things like SD-WAN software. Simplifying the role of any remaining hardware, such as an internet router, also reduces the cost of maintenance.
Of course, most large enterprises that have built a WAN will continue to need one for years to come. They have sites that mostly talk to inside resources, for example, or cannot accommodate internet-level variability in performance between the site and the resources in data centers or private clouds. Or they have compliance or security features that cannot be met with bare internet connectivity -- yet -- or that will take years to migrate.
Even companies that have to stick with WAN services, though, may soon find they can pull the WAN out of the majority of their smaller sites and still meet bandwidth and low-latency needs.
In fact, given the viability of remote work, it would not be unreasonable to see most companies invert the order of consideration when mulling branches and networking in the future. Instead of asking, "Does this branch require a WAN connection?" organizations might ask, "Do I have enough use cases requiring a WAN connection in this area to justify creating a branch here?"