Why there is a shift from SQL only server to Aerospike or Crate which are hybrids?

What are the use cases where hybrid databases like Aerospike and Crate would out perform compared to SQL DBs? Can someone who have worked with any one (or both) list down the pros/cons of using such DBs?

Will migrating from MSSQL to Aerospike require much of an effort? or will it be even feasible?