The Samples Written metric represents the number of pixels/samples written to render targets.
The graphics driver 9.17.10 introduces a new notion of deferred clears. For the sake of optimization, the driver decides whether to defer the actual rendering of clear calls in case subsequent clear and draw calls make it unnecessary. As a result, when clear calls are deferred, the Graphics Frame Analyzer shows their GPU Duration and Samples Written as zero. If later it turns out that a clear call needs to be drawn, the work associated with that clear call gets included in the duration of the erg that was being drawn when this clear call was deferred, not necessarily a clear call. This means that in the Graphics Frame Analyzer metrics associated with a clear call accurately reflect the real work associated with that erg.