[Reference:https://community.splunk.com/t5/Getting-Data-In/Why-does-Splunk-have-multiple-indexes/m-p/12063, , Different retention times: You can set different retention policies for different indexes, depending on how long you want to keep the data. For example, you can have an index for security data that has a longer retention time than an index for performance data that has a shorter retention time., Restrict user permissions: You can set different access permissions for different indexes, depending on who needs to see the data. For example, you can have an index for sensitive data that is only accessible by certain users or roles, and an index for public data that is accessible by everyone., , ]