I could not agree more with maybe a little reservation. Nothing irritates me more than to open up conduits, troughs, JB's, and even panels to discover miles of unused and abandoned wiring. I consider that to be a sign of laziness on the part of my precursor on the job. Granted, a lot of wiring is left in place for future use. At the time that wire is no longer going to be used, it should be removed. I have run into many instances where old wire has been left in conduit and the new replacement wire ahs been put in the same conduit. It only makes sense to me to remove the abandoned wire and I think it makes for a neater, more professional job.
