Use the split screen to compare two tracks, such as an online and offline version. Generally this is used to compare a rough cut to the final assembly. By merging both tracks into a single image, you can compare the two for editing synchronization, color matching, etc.
The split screen compares versions as well as video tracks.
To compare tracks in split screen:
Depending on the split, you will have different attributes available to change the partition between the two clips. Modify the values in these attributes to provide the best comparison.