Not necessarily. I have many of my cameras setup to view a wider area, so sometimes there might be some movement off in the distance that I want to capture, but is too small to set off the motion detection (based on how I have it setup). Therefore, I know that the motion will be captured in my continuous video file once I narrow down the correct time frame even though there is not an alert for it.
Like @fenderman said, as long as you set it up to capture what you want, then it will work wonders for you.
