This is a feature that I never used. So I can't say that I'm particularly sad to see it's removal on May 5, 2015.
"Three and a half years into this journey, we’re looking at what the users are telling us Google Plus is good for, and doubling down on those uses. For instance, one particular use-case on Google Plus is people aligning around common interests. If I’m interested in astronomy and I want to meet other people interested in astronomy, we think we have a good solution — Collections, a new feature that we launched just two weeks ago. It’s the first in a series of pivots. We’re also moving aside the things that either belong as independent products, like photos, or eliminating things that we think aren’t working."