Any device connected to the hotspot’s Wi-Fi network will not realize that it’s actually connected to a cellular data network. It will behave as if it's connected to a Wi-Fi network (which it is), so any settings that usually restrict data access when connected to a cellular network will be ignored.
To reduce excessive data usage, we suggest turning off push notifications for email and social apps, closing non-essential apps and browser windows, and powering off the hotspot when you don’t need to use mobile data.
Additionally, when using a laptop, turn off any cloud backups, e.g. Dropbox, OneDrive, CrashPlan, which can use data in the background.