I have been editing my Titles and Descriptions. Occassionaly, I had to preview some of the video to get an idea of the content. Most of the time, this took about 5 seconds of each video. According to my account, I have already used half my month's allowable. I don't believe that the system is recognizing that I only viewed ("USED") a portion of the video. Instead, it seems that the system is calculating what has been downloaded or already streamed. I believe that is a perversion of "only pay what you use". I didn't "use" it if I didn't view it.
We mean that you only pay for the amount of data that gets transferred, while, with most other services you pay a fixed amount per month no matter how much gets streamed, even if you stream less than your allowance.
With Bits on the Run you don't have a monthly allowance, but rather you purchase balance that carries over to the next month if it doesn't get used.