The card in your ST10(+) that records the telemetrics is the only way to diagnose a crash or a fly-away. Without it, no chance at warranty repairs as no proof it was not user error. It also includes lower quality video from the camera. Personally, I wouldn't fly without one. It doesn't have to be large, 8 GB or so. It also does not have to be fast as it isn't recording 4K.