I primarily use the solution for business related chatting. We use it mainly to publish and to have social communications on the business side. On a business level, it's used for the internal team to publish their opinions or their ideas, and share them to the group.
The design of the solution is its most valuable feature.
Yammer shall not stay an independent non integrated service and shall not duplicate what team and outlook services do - it can be the heart of outlook conversations / publishing
I've been using the solution for a couple of years.
I've found Team or Skype for Business are more useful than Yammer.
I'd rate the solution three out of ten.
I did not find Yammer too useful for my type of business. You cannot sell a Ferrari to someone who does not drive very fast, for example, as they would give Ferrari a low rating because they aren't using as it's meant to be used. For my type of business, I need something to be more flexible on integration. I'm not on the marketing side and do not need to publish something on Yammer for everyone to see, or for everyone to share their opinion on.
If Yammer were to have more integration, the product might be more useful for me. I'd probably rate it at a nine or ten in that case. However, for me, in terms of helping my type of business, it's not ideal and I'm rating it rather low.