Invision community says that they offered to up vote answers and allowed marking an answer as the best answer for years now. This, they are proud of their Q&A ability. But now Invision Community is talking about marking topics as solved added to v 4.5
This new feature allows the topic starter or your community management team to mark a post as the solution. This highlights the post within the topic as well as adding an icon to the listing views.
The green tick icon tells you that the topic is solved. There will be a recently solved feed and members will be associated with solved topics. Also, the author of the best answer post will get an in-board notification
It may be that Invision thinks that will make the post author happy. I don't doubt it at all. Some recognition is always nice.