Imagine one of those 4ft led shop lights with a 6 foot plug-in cable that you can get from anywhere. If you had a basement with finished walls and floors but an unfinished ceiling with electrical outlets up between the joists you could simply hang the light where you want and plug it in and you're good to go, right?
Ok, so now imagine you want to do the same thing but instead of that 4ft shop light you want to use recessed light housings or retrofit kits. Rather than hardwire the housing or jbox though I would wire them up with 12 ft cords with plugs. This way I can mount the housing/retrofit wherever I want and simply plug it in like any other hanging lamp, right? Or no?
The reason why is that due to the size, shape, and ducts/obstructions in my basement it's not very clear how many lights I would need nor where they should be placed for best coverage. However if I can move the boxes around and simply plug them in then I can start with a reasonable best guess and then expand the system or relocate individual lights as needed.