SeaSaltIceCream There will be some features missing in at least some of those applications. Maps, for example, will not be able to store offline maps and will not be able to save addresses. Photos will not be able to sync with gaccount (which is probably a good thing anyway). Certainly nothing there that I would consider worthy of installing gservices.
Now some other software will have a harder dependency on gservices for normal functionality. Often things that provide instant notifications, since the notifications will be delivered THROUGH g. g advertised this feature as if it was to benefit the user, but the reality is that they serve notifications this way in order to try to force people to use their binary software. So sometimes it can be a bit of a challenge to find alternative software that works to deliver notifications without the dependency on g*.
Now some software will complain that it requires gservices in order to work, but still works despite that. All of the banking software that I use are examples of that. Start the program, it nags you about gservices, you press OK or whatever, and you're off to the races. Just an annoyance.
For my own use, I do NOT have gservices installed. No need for my use, and frankly, I don't trust them.