Having trouble with these settings, they seem contradictory?

[klepp0906]

My big issue is I want to make sure that under all circumstances - whether im adding files, or especially if im removing a disk, or scanner is evacuating due to a problem.. that my disks are filled in order and go based on the hierarchy I set in the ordered file placement plugin.

In order to accomplish this I moved that plugin above the scanner plugin and those are the only 2 I have checked.

The following settings give me pause though. 

 

It sounds to me like the first checkbox says "drivepool wont do anything that the plugin doesnt say to do" which in my case means put data on the drives I choose in the order i choose.

then it sounds like the second checkbox says exactly the opposite.   

can someone differentiate a bit better for me?  I realize im likely conflating "limits" and "rules" but i beyond that im at a loss.   Then of course the "unless is being emptied" is of primary concern considering I want to make sure if a disk starts to die things arent flung all over hells half acre

[Christopher (Drashna)]

Real-time placement limiters are different.  They're mostly used by the Stable Scanner, Ordered File Placement and SSD Optimizer balancers to ensure that no files are placed on these drives.   They're the "red arrows" you may see on the drives.