Search Before You Post
Before publishing To a Community, yammer would search to see if that question has already been asked or answered and provide results that may answer the question, and if there is no match to continue with publishing.
Rik de Valk commented
Showing similar existing questions when typing a new question is essential for a Questions feature. Otherwise questions will be asked multiple times and information (answers) will be scattered across questions.
This is an absolute must have!
See Stack Overflow.
Also see these suggestions: https://yammer.uservoice.com/forums/399627-yammer/suggestions/19335211-use-yammer-groups-for-developers-q-a-like-stack