Not knowing for sure of the exact reason the plastic pan is there, I would have to fall back on rule number one for contemplation of removing parts from vehicle. If the manufacturer did not think the $.50 piece served a worthwhile function, you can bet the manufacturer would not have put the $.50 part on there.
reference the changing of oil top vs. bottom; I personally prefer the good stream effect (that I feel flushes the bottom of the pan with a good current or flow) that you get from the drain plug. Also, I have the vehicle tilted toward the plug during draining (some from rear wheels, others from front wheels). Also, I have found tell-tale signs of engine condition from draining at the plug: I once found a cotter pin from a connecting rod bolt on my airplane. I used a strainer to catch whatever comes out. Needless to say, I popped the cylinders off and put in the STAINLESS cotter pins that should have been there to begin with. On another occassion, I found a tooth from a sprocket in the oil of a M/B. FWIW.