Video is a data intensive activity. Engaging in data intensive activity during a time that your Anytime Bytes were depleted would cause the SmartBrowse feature to kick out and normal FAP speeds of approximately 150 Kbps to kick in.
There are three meters available to you to help monitor your data usage. How you spend that data is up to you.
There are a number of things that you can do that will reduce the data used on unintended areas such as blocking ads and scripts among other things.
You can of course purchase extra cost blocks of data known as "tokens".