If you are using this proxy on a limited bandwidth hosting, the amount of internet data you use will affect the bandwidth usage as you are using the data allocated to the hosting account. When people visit your site, your site is downloaded in their browser and what your hosting server does is upload the data and your device downloads it.
But here, you are downloading or uploading, you browse a website and its downloaded in your hosting server then uploaded to your device browser, it is even doing both 😀
So if you download a 1GB file in the proxy, your server uses 2GB splitting it as downloading the chunks of data and sending to your device.
Let me know if this makes sense now. 🙂