Product Feature: DataFlow Server
A cache group defines access to shared cache resources on the server machine. Cache groups enhance performance because the Data Flow Service can store and retrieve results directly from cache. When you configure the Data Flow Service to treat cache as sensitive to groups, members of cache groups can retrieve stored objects and query results directly from cache.

There are two things mainly to observe:

Actual number of user logged in to DFS you can check from user pool.

There are two things mainly to observe:
- users/clients connecting to DFS
- client sessions created by users
Actual number of user logged in to DFS you can check from user pool.
UPDATED:
August 31, 2017