How do you balance speed and capacity where it makes sense to use anything but the largest one?
Now, with the gap so large, 80-240, there's cleary a time to use either; the lithus is only like 25% slower for 3x the capcity, so anything over 80u is a no brainer to use lithus.
With modules, if you take them on/off, there's a chance that you won't have the size you need, where you need it. If there was a 360U at 50%, it would just be always installed on the lithus, because the small speed hit is offset by always having it when you need it. So the 240U and under modules would go unused, so your basically just changing the Lithus to a 360U hauler with lower top-end speed.
Sure, there's probably a few situational scenerios where you could use a 120 or 240, but the majority of the time your just going to max it out, because bag space is always important.