I've been searching on the internet about using interval ajax polling for live web pages and I've been using it along with SignalR. Now I always read an article online about using ajax polling for live web pages that there could be an impact on your server or maybe there's a downside effect when using ajax polling if you have heavy traffic on your site and/or when you're polling large data from the database.
If this would be true, I guess my questions are, what are the server impacts that they are talking about that could lead to any downside effect on your site? and how to avoid those server impacts if you choose to use ajax polling for your live web pages?