Why not drain pink antifreeze right away?

After running the anti-freeze through, I put the jug under my low-point drains and get a little out of the lines. Then, that gets poured into the shower drain.

I drain mine into the empty anti freeze container and then use it to pour into the P traps.

AFAIK there is no reason to keep the antifreeze in the pipes, but you should keep it in the P traps and the toilet. Also some in the tanks. That said, I have always left the antifreeze in the pipes. I guess by the time I have reached that point I have had enough.