My take on taking care of cards.
Back in the day, "Bee" brand was the quality deck to use. Speaking from a mechanic's point of view, the newer the cards, the better one could operate and operate smoothly. I guess this would be the same for doing magic tricks and demos.
I would never play using old cards. New deck were in order, and then after time, they are discarded. New cards are predictable on how they will act when you manipulate them.
Sometimes I would have to deal seconds around three or four players, sometimes more.. It is essential that the tools I am using are in the best shape. Older cards that have been used a lot will tend to stick. In dealing seconds you want everything to be smooth. No sudden moves, no fast moves, nothing to arouse suspicion. Playing with older cards would be just asking for a mistake. In arena I played in, you make "no mistakes".
Cards that have been used for a while, in my opinion should be discarded. Used them for practice or give them to kids to play kid games..
Just the opinion of an old geezer...