When you click that button, it turns into - Quote and every post that has the multiple quote selected, will be added to your next post when you click "Add Reply".
You can also use it to quote posts from one thread to another. Just click the Quote, and go and click "Add Reply" in another thread, you'll have that post quoted in the other thread. It's most useful when quoting posts from Locked threads, like this quote from SRP Closure thread which is locked:
' Wrote:The special RP forum is now closed. Pending SRP requests will not be processed but might be at some point in the future.
When you click that button, it turns into - Quote and every post that has the multiple quote selected, will be added to your next post when you click "Add Reply".
You can also use it to quote posts from one thread to another. Just click the Quote, and go and click "Add Reply" in another thread, you'll have that post quoted in the other thread. It's most useful when quoting posts from Locked threads, like this quote from SRP Closure thread which is locked: