I use it specifically to show the missing data on the SPY as compared with the continuous data on the SPX500 .
If i pasted this picture correctly the chart on the left is the SPX500 and on the right is the SPY. Notice on the left chart each shaded area has two blue vertical lines and the chart on the right appears to have only one blue vertical line. In fact there are two lines on the right chart as well. They are laid over each other is all. The same script if applied to both charts. The chunk of data between the two bars on the left chart is simply just not recorded on the chart on the right. The grey area on the right hand chart is there because i have the extended hours data button pressed so it reflects in the graph.
Often what appears to us as a gap on the SPY chart is smoothed out and explained by the continuous data on the left hand chart of the SPX500. There really is no "gap" really, only a lack of recorded data on one chart compared to the other.