The only limit is the amount of data you have. For example if you are on the Mini 4GB plan, you can use all 4GBs to tether your phone data to another device.
Please note that if you are using your hotspot for devices such as laptops and televisions, your data is not throttled and running at 5G/4G speeds. You may experience your data allotment running low quicker than normal if streaming. Allow your usage within the Brand Mobile app to sync prior to resuming any data sessions to view up-to-date data usage.