We have got burnt a few times abroad when our laptops decided to download big updates when connected via our mobile phones. That's why we definitely wanted to have a control of data use in Private Spaces.
At the moment, the main page of your private space (http://private.space) shows your actual data usage so you can easily check if your laptop, or mobile phone is, for example, downloading a big update when you are abroad.
We are considering an option to limit daily date usage on devices. If you are interested in this, please let us know by emailing to firstname.lastname@example.org, or creating a new support ticket - the link is at the top of this page.