Summarize local routes towards overlay to reduce the route prefixes advertisement 

Large prefixes advertised over overlay to Branch sites.

Causes best selection for specific prefixes routes

Route summarization on a Mist Session Smart Router (SSR) refers to the ability to condense multiple network routes into a single "summary route" to reduce the size of routing tables and optimize network traffic, essentially grouping several smaller networks under one larger prefix,

How to configure :-

• Access the Mist portal. 
• Navigate to the relevant network configuration section. 
• Specify the IP addresses and prefix length of the routes to be summarized

Route summarization is typically done on the edge of a network, where multiple smaller networks connect to a larger network.