Did some research and this is what Hola says to the question of data usage:
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Will I consume more mobile data on my Android device because of Hola?[/h][COLOR=#333333][FONT=PT Sans]
No. Hola actually reduces your mobile data usage through better, smarter data caching. Expect to save between 20-30% of data usage after a few weeks Also, your phone only acts as a Peer on the Hola Network when plugged in to a power supply and when connected to the Internet over a Wi-Fi network.
From this I take it that if you disable Hola or close the browser that's running it you will no longer be a peer in that network and hence no longer be transmitting data amongst the nodes. There is also the possibility of checking usage stats (up/downloads) to make sure. Whether it will give the promised 20-30% increase in speeds is questionable but hey - use it or don't.
What do I know?
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