Virtualization has originally been a trend in compute.  Servers became virtual machines which allowed automated provisioning, load balancing and management processes. Hypervisors could manage a variety of virtual machines and improve performance and scalability. Network and storage assets were rather slow to catch on.  Software defined technology stack aims to virtualize compute, network, storage and security aspects. The primary benefit of SDN is that it makes provisioning dynamic as opposed to the static configuration from physical resources. Moreover, connectivity can change as compared to networks that were usually designed with fixed pattern. SDN helps to manage complexity. It performs segmentation, workload monitoring, conditional forwarding, and automated switching for dynamic optimization and scaling.
Software defined storage SDS represents logical storage arrays that can be dynamically defined, provisioned, managed, optimized and shared. Together with compute and network virtualization, a software defined datacenter SDDC tries to eliminate virtual servers, private clouds and hosted private clouds that have significant physical resources.
We should recognize that SDDC does not replace all of the IT assets because existing infrastructure may have deep connections. However, it does offer a newer simpler paradigm for workloads to migrate to and newer ones to be written. Generally the strategy determines the activity and the modernization.
SDDC attempts to reduce TCO with the retirement of equipments and does away with their operation costs. Moreover projects generally see an improvement in performance and scalability with SDDC.
There are three types of usage of SDDC - infrastructure, application development, and production support. Software defined stacks also remove recurring costs.
Courtesy : software defined everything by Bawa and Clark