When I created the Process List command, I imagined it might be used for additional processing of some sort. And I think the documentation here may be confusing.
In practice, I found that when I used Process List, it only included the single Find/Replace action. And it seemed silly to make users add two actions all the time for the most common use-case. That is why I re-instated Find & Replace with List.
The warning is not about mixing the two within the same cleaner, but just understanding that Find & Replace with List is trying to operate on a list as well.
For example, in this setup here, if both First List and Second List have 4 rows :
Because it is inside a Process List, each of the 4 rows in "First List" are iterated through, calling the actions, including the Find and Replace with List for each row (this action then runs through each of the 4 rows in Second List). The result is 4 x 4 rows or 16 find and replace actions applied instead of 4. That's almost certainly not what you want.
If anyone can think of some additional use cases where Process List might prove more useful, please let me know.