In a sequence you could have a few targets that you wish to prioritise over others but their imaging times overlap, for example in my sequence
Crescent Nebula (Narrowband) Start time of 19:40 and end time of 22:10
Iris Nebula (RGB) Start time of 20:28 and end time of 00:28
Elephant’s Trunk (Narrowband) Start time of 21:00 end time of 01:00
Dark Shark Nebula (RGB) Start time of 21:42 end time of 01:42
As you can see that’s just four of my targets that overlap, now on nights when the moon is pretty illiminating, I would rather focus on narrowband targets, but on less moon illuminated nights I would rather target RGB images, however there could be “Spaces” (No pun intended) between the RGB images where narrowband data can be acquired, so in the above, if say Iris had a priority weighting of 1, and Crescent had a priority weighting of 2, the sequence would look at the start times of both and then stop imaging narrowband on Crescent at 20:28 in order to start serving a higher priority target without having to change the start/end times
I hope that makes sense, it does in my head 