If you are not viewing the live stream, the camera uses a minimal amount of data for its digital heartbeat. If sound/motion detection is turned on, then only 12 seconds of video is uploaded to the cloud at most every 5 minutes.
If motion/sound alerts are turned off, then no data is sent to the cloud, other than the heartbeat mentioned above. The video records to the mSD card completely independently of whether motion/sound alerts are turned on or off. You may set the mSD recording to happen continuously or only while motion is being detected.
For info on quantitative data usage, click Support at the top of this page and then click FAQ. This and many other questions are answered there.