This is kind of hard to explain.
Suppose you are automating the volume for a track, and are making small adjustments, like 0db to 1.5 db. In the arrange view you can barely see this shift in the orange line, and doing any more detailed automation requires expanding the individual track window. The window provides automation from -inf to +6db (for volume in this example) but most automations occur between -10db and 0db (volume adjustments between parts).
If there was a magnifying glass like function within the track windows in arrange view you could easily zoom in on an area within the range of the parameter being automated, making very detailed automation possible.
It could be right next to the circle with the + sign in it, you know the thing that opens new automation windows.