Why SDWAN ?

 Year 2008 :

3 or more remote offices for company ABC and all user are using three major type of services : Email , ERP , custom APP and all server are hosted in Datacentre . If some of user want to access internet they have to go Datacentre and from DC it will go to public Internet . Company ABC choose only one entry point from outside and all security hosted at one place ie Datacentre ( internet traffic will go from remote site to DC then internet cloud ) . all transport link are MPLS from remote site to DC due to high reliability and high quality but cost/ BW is very high

Year 2018 or after that
people started implementing office 365 ( Saas ) instead of MS exchange server , Salesforce Saas comes in Picture for ERP and other application hosted on AWS or Azure

Now MR SDWAN ( cisco) pops up with following attributes:
control plane and data plane segregation
different level of security at end points or edge location only
centralised control plane and policies lot of action can be done in terms of application
local internet breakout
saas application can be directly access by local internet breakout
policy ( localized , control)
application aware routing : select your transport link according to application at each site.
service like saas on ramp and IaaS as ramp