The Composer window in Color Correction mode allows you to view material from three segments at once in three separate monitors, making it easy to compare material on a shot-by-shot basis.

By default, the left monitor shows the previous segment (the segment before the current segment), the center monitor shows the current segment (the segment the position indicator is on in the Timeline), and the right monitor shows the next segment (the segment after the current segment). See Understanding Default Monitor Display.