I can't count on them not breaking notifications (such as those for when I receive a message while signed out) in new and exciting ways at random times, and... well, it's just terrible in all kinds of ways.
And as with other things smushed into Google+ at one point or another (see Voice, Reader, Picasa, etc), a lot of users of the old thing will tell you that the old thing was actually superior to what wound up in Google+. In the case of Latitude you could easily share the information in a general way to all of Google Maps which covered a lot more platforms than Google+ itself does.
[1] http://www.androidpolice.com/2015/07/20/apk-teardown-google-...
If I add you to a circle, what happens? Are you now part of a known group? Are you just secretly tagged for my convenience? Can you see my profile in full because I added you? Can I see yours?
iOS users can use the "Find My Friends" app for the same purpose. It is a huge time saver (and safety tool) for my wife and I. I don't like calling her when she's driving to ask how far she is from home. One quick look at the app and I know when it's time to get the baby ready for dinner.
Hangouts is great. Remember that Hangouts launched as a part of Google+ before breaking out.
Ironically, Google+ Photos is also one of my favorites. If you snapped photos on a vacation, you may return to find that Google has stitched them together into a "story" -- including where you were when you took photos, who you were with, etc. It's a nice way to relive the memory.
Circles is also a very simple concept for social network security. It's easy to understand, and I like that Google left it out in the open as something you should definitely do. Facebook has a similar feature, but it's not in their best interest to highlight it.