Samples the result of what one pixel represents in time. This may not accurately reflect the actual animation (especially if you are zoomed out). However, by adjusting the sampling rate, you can choose between curve accuracy and update time. A higher sampling rate means more accurate representation but longer computation time.
When screen based sampling is turned on, the sample rate specifies the number of pixels per sample. When it’s turned off, the sample rate specifies the number of frames or current time units per sample.