Session recording captures a screenshot of your page then mouse clicks, scrolls and coordinates as well as keystrokes if enabled. This data is then replayed across the screenshot in the playback window. The process is very efficient and should not require any further resources than normal. Session recording is not captured in a video format such as AVI or MP4 that can be downloaded.
Sessions are stored in the database and aren’t too large. The exact size depends on the website and the number of average page views. They are stored efficiently to minimize storage space. For example they are compressed (like a zip file) and the same stored recorded HTML is re-used again whenever possible. Also when a recording is deleted later, they will be completely removed. So even storing 100.000 and more recordings will not be an issue.