Just FYI, I have 5x1080p, 1x960p, and 1x720p all recording 24x7 to a 3TB drive, and have room for a full week's worth of recordings.
Even though I feel that motion capture is pretty good, I still find there are times when I really appreciate the ability to go back and review footage for events that failed to trigger an alert, or that were buried in a bunch of alerts that were triggered by shadows from wind blown trees, or by light changes from clouds.