In case when dynamic snitching is enabled data is read from 'the fastest replica' and other replicas send digests for CL=QUORUM/LOCAL_QUORUM .
When dynamic snitching is disabled, as the concept of the fastest replica disappears, which rules are used to choose from which replica to read actual data (not digests):
1) when all replicas are online
2) when the node primarily responsible for the token range is offline.
There are reports (in this ML too) that disabling dynamic snitching decreases response time.
What effects stand behind this improvement?