Group by, Memory Group by Plugin

What is the difference between Group by and Memory Group by Plugin except from sorting?

Hi Dnyanada,

Memory Group by step groups rows based on specified fields. This step builds aggregates in the same way as group by step. However, it does not require a sorted input since it processes all rows within memory.
When the number of rows is too large to fit into memory, you need to use the combination of the Sort rows and Group by steps.