The Chase tool can be used to take a pattern and “chase” it through several channels over a time range.  For example:

Before a chase…

… and after a chase

Exactly what is chased, and where it is chased to, depends upon how you click-and-drag (or, if using the keyboard, how you expanded the selection).  The lighting effects in the corner that you started dragging from will be chased to the corner that you finished dragging to so that, for example, you could chase effects “up” or “down” through channels.

The effects that are chased will include everything up to and including the last non-off lighting effect in the channel that you start dragging from (or, if dragging backwards, everything from the first non-off lighting effect).

The Chase tool can also be used on RGB channels:

Before an RGB chase…

… and after an RGB chase

The Chase tool pays attention to the Paste from Foreground clipboard option, so that you can chase a pattern without overwriting existing effects with “off” effects.  For example, consider the following sequence, and imagine that you want to chase the second fade up in the first channel:

Before chasing the second fade

If you did not have “Paste from Foreground” turned on, the chase would overwrite the ends of the existing fades in some of the other channels:

After chasing the second fade, without “Paste from Foreground”

But with “Paste from Foreground” turned on, the existing effects would be kept in place:

After chasing the second fade, with “Paste from Foreground”