It allows for managing indexer/tracker from only one place for all *arrs. I usually set the apps to “Full Sync”, so I never change anything in each of the apps (e.g. radarr).
It also provides some statistics, like how many file grabs each indexer gave you compared to others. This might help to decide which of the paid ones are actually useful (useful for usenet indexer).
If your not resource constrained (e.g. rpi), I’d recommend prowlarr. It makes things more streamlined imo.