I came across this post which has this answer from @strcat
and I need to break it down to make sure I understood it correctly
Many of the other libraries such as Google's Ads SDK provide fallback code and work without Play services being present.
Apps can use Google services without Google Play being present. You can see that Google Maps completely works without Play services with only a few missing features, as a nice example of how it's not required. The Google Ads SDK works fine without Play services too. Thinking that not having Play services means apps aren't able to use Google code and services is very wrong. Play services on GrapheneOS is a regular sandboxed app. It has the same app sandbox and restrictions as every other app. If you install an app like Discord using the Play SDK, Google Play already has code execution within the standard app sandbox through Discord. Whether or not you install Play services for Discord to be fully functional is up to you, but if you think you're not giving the Google Play code as much access by not installing it you're wrong and are misunderstanding the whole sandboxed Google Play approach.
So, in a nutshell, unless I am very mistaken, what they are getting at is that a grapheneOS phone without Google Play Services is still completely capable of running any apps that use Google SDK. The only blocker really is if the app itself will not launch without Google Play Services installed and running.
So, Google's Ads SDK and Google Maps, both are apps that can work without the Google Play Services. You will still get ads in the apps that utilize that Sdk and the Maps app can still run for the most part. The only thing they can't do is run any part of the code that require Google Play services to be installed locally, get access to any non-resettable hardware identifiers and any user-data (unless the user specifically grants the app access to the data)?