Andy Wolber offers four reasons you may want to create a Google+ Collection.
The new Google+ Collections feature, launched in May 2015, gives you a new way to group your posts. Create a Collection, then when you post a new item to the Collection, the items shows up in the stream of people who follow that Collection. (Note: As of May 2015, Collections works on the web and on Android devices, not on iOS.)
The feature works much like a Pinterest board. For example, I pin each illustration I create for my articles to a Pinterest board. People who follow that board are notified of each item. People may choose to follow everything I post or just follow the board where I post my illustrations.
You choose whether to share each Collection you create publicly or restrict access to the collection to your organization, a specific Google+ circle, or specific people you select (Figure A). You can even create a private Collection that only you can see. As of May 2015, you can't change the visibility of your Collection after you create it. (Workaround tip: Share a collection with a Google+ Circle, then modify the membership of the Circle.)
Choose to share your Collection publicly or restrict access.
Here are four reasons to create a Google+ Collection.
1. To share a single link to a set of resources
For example, you might share posts related to Google Docs, Sheets, or Slides to a "Google Apps Tips" collection. Since each Google+ Collection has its own link, you can share the link to point people to your collection of Google Apps tips (Figure B). They'll see the most recent tips listed first.
Share the link to your public Collection.
2. To reduce "noise"
If you post information relevant for distinct groups, use a Collection to target your message to a specific segment of your audience. A school district with three schools might create a Collection to share news related to each school. School-specific items could be posted to each individual school's collection, while general interest items might be posted without classification.
3. To share privately
A Collection may also serve as a way to share information privately. A Collection could help track a competitor's activities or gather new product/service ideas. Both are the types of posts you might want to share with colleagues, but not the public. A private Collection--shared just with yourself--might even serve as a personal journal.
4. Collections as a courtesy to your followers
You might create Collections as a service to your readers, much like a newspaper separates articles into sections (Figure C). For example, separate Collections could allow people to choose to read your technology-related posts, your sports fan-related posts, or both.
Three ways to add a post to a Google+ Collection.
Google+ Collections for work
Organizations that use Google Apps for Work may find that Collections make Google+ more useable as an enterprise social network. Before Google+ Collections, every post from a colleague would appear in your stream. Now, you can follow only those streams of posts you want to see from your colleagues. With Collections, you can separate your posts into streams that serve your teams.
Finally, for people who may not spend a lot of time working with Google+, the difference between Google+ Collections and Google+ Communities might be unclear. Both offer a way to share a post with a set of people. But there's a key difference: a Google+ Community gathers people. A Google+ Collection gathers posts. To organize people, create a Community. To organize ideas, create a Collection.