>>105780747It depends on whether you mean installing a custom OS, or completely removing Google Play Services from your device.
LineageOS is the easier part, because most users install Google Play Service blobs right after their OS install. For a while LineageOS even included this as a built in default.
To me, this defeats the purpose of using an alternative OS, so I haven't installed Google Play Services.
Without Google Play Services, I have encountered just two drawbacks that are not able to be resolved with an acceptable effort/pay-off ratio:
>NFC paymentsI never used these in the first place, as I got into this stuff before it was widespread and I had a phone with NFC, though I would have liked to.
I believe it is doable to get NFC payments working on custom OSs, but you will need Google Play Services, and you'll be playing a bit of a cat and mouse game with Google too. Chasing the next workaround for passing SafetyNet, device integrity, etc.
I think it requires a locked bootloader these days too, which is sometimes possible with a custom OS if you're device supports relocking the bootloader.
I have a MagSafe case with my contactless debit card in there. Not as good as NFC but acceptable.
>Google mapsIt's easy to use with Google Play Services on LineageOS, but without them, you can't.
I use OrganicMaps as a replacement and it's as useful as Google Maps in most areas and even has a few advantages in things like offline maps and the amount of small footpaths and tracks that have been logged on OSM, but it is does lack a couple of features that Google Maps has.
It doesn't have traffic updates, and it can't do public transport pathing (though there is a slow moving but not dead issue building towards a robust solution for this.)
Other than those two things, I don't notice any missing functionality, though I've made sure to stay well outside of the Google ecosystem, so if you're already in there you'll probably encounter more problems staying in there effectively.