I’m currently using approximately 15 MB of data transfer per month, so I’m not worried that I will exceed the limit. 
But just in case that I would exceed the limit, it would be very bad. 
I figured out there is a way to prevent that from happen, Bandwidth Throttling. 
What would happen if I did not set up a directory called mydomain.com.throttled? Would Bandwidth Throttling not work? Or would visitors see a not found message? Or would anything else happen?
If your credit is good and your server handles the load, they’ll probably just charge you for the extra.
If the server can’t handle it, or your credit is not good, then they’ll probably disable your site or the part causing the load, at least temporarily.
You are welcome to a refund.-Michael;Comparing ‘DH of today’ with ‘DH of old’ does not serve much purpose.-Dallas
Okay. But if I turn on Bandwidth Throttling and does not set up the folders specified in the panel that visitors is supposed to be sent to when my custom Throttling limit is hit. Let’s say that I set my Throttling limit to 1200 GB, that will give me a little more than 800 GB before I hit the hard limit. What will happen then? Will there be a 404 message or does BW Throttling depend on those specific folders to work?
I believe the throttling works anyway, but your users just won’t get a nice page to tell them about it. I’ve not tried it though, and it seems odd not to provide a page. It’s one or two sentences on a basic html page, so it isn’t hard to set up.