What is Firebase App Indexing & what good is it to me as an Android owner?

Here's all that I know about it by looking all over my phone for it.
1. Settings > Google > Firebase App Indexing > Capture user actions & errors
Enable collecting & displaying recent User Actions & errors = off

2. Settings > Google > Firebase App Indexing > {choose a listed app}
a. Clock com.google.android.deskclock
(lists all my alarms recently set and all my stopwatch activities)

b. Google Play Services com.google.android.gms
(lists my entire contact list & all music I listened to & all my apps)

c. Maps com.google.android.apps.maps
(lists exact addresses of all the places I've routed Google Maps to)

3. This clears the "Clock" & "Maps" Firebase (but not Google Play Services)
Settings > Apps > {app} > Storage > Clear cache (did not clear firebase)
Settings > Apps > {app} > Storage > Clear data (cleared firebase)

This cleared the data (momentarily) for Google Play Services
Settings > Apps > Google Play Services > Storage > Manage storage
Press the "CLEAR ALL DATA" button.

4. But both detailed listings returned within a minute of clearing them!
MobileApplication = 237 (lists all my apps)
Person = 222 (lists all my contacts)

Each of those says it last sent all the data to "someone" a week ago.

I don't worry too much that the Google Firebase App Indexing is sending
to someone (I don't know who!) all my applications but I do not like to
see it sending every one of my contacts to someone I don't even know.

Who is this Firebase App Indexing sending all that data to anyway?
How do I completely turn off this Firebase App Indexing on Android?