It means you should not needlessly reply to years-old threads, as doing so "bumps" them to the top of the list of current posts. Additionally, someone who posted something in 2014 may not even be an active member here anymore to see your reply.
If you have a question about something that hasn't already been covered, feel free to create a new post in the appropriate section of the forum. If it relates to an old post that you think is relevant to reference, you can include a link to that old post in your new posting so people can easily see the old thread you have a question about.