A snitch determines which datacenters and racks nodes belong to. Snitches inform the database about the network topology so requests are routed efficiently, and enable DataStax Enterprise (DSE) to distribute replicas by grouping machines into datacenters and racks. Specifically, the replication strategy places the replicas based on the information provided by the new snitch. All nodes in a cluster must use the same snitch. DSE strives to not have more than one replica on the same rack (which is not necessarily a physical location).
If you change snitches, you may need to perform additional steps because the snitch affects where replicas are placed. See Switching snitches.