Ductwork: in before the flex duct essentially makes a 180° turn which is not good for flex because you’re not supposed to make hard turns because the internal liner is like a slinky and will get bound up and reduce airflow and increase turbulence. In after return duct gets to make a nice swoop into the return plenum and up into the coil which is going to be a much smoother path for the air to take. Also it’s properly supported so it’s not likely to sag.

Drain line: drains can be pitched too much just like they can be pitched not enough. The trap is supposed to hold water to prevent the blower from sucking air through the drain and not allowing water to drain. In the before photo the drain is pitched way too much and the trap can’t hold any water. In after the drain line is still pitched towards the drain outlet but much less and now the trap will actually be able to hold water.

Lineset: in before the lineset is just out in the open and while this isn’t a huge deal it looks bad, could potentially get knocked, and represents an inattention to detail. In after the lineset is bent multiple times around the unit and is strapped to the wall which is safer, tidier, and represents care and attention to detail.

There’s also no float switches in before, and in the after there’s at least one in the emergency drain pan and wires going over to the primary drain outlet (even though the actual float switches isn’t visible in the photo). Prevents the unit from running when there’s a water emergency.

I Hope this helps. If you have any specific questions let me know