When you define a whitelist, Splunk Enterprise only indexes the files you specify. When you define a blacklist, the software ignores the specified files and processes all other files.
It is not necessary to define both a whitelist and a blacklist in a stanza. They are independent settings. If you do define both and a file matches both, Splunk Enterprise does not index that file as blacklist overrides whitelist.
So I suggest to use either whitelist (only index specific files) or blacklist (ignore specific files). I don't see any reason for using both.