Definitely worth keeping if selliing it online is going to be an option when you get rid of it and need to courier it somewhere. Trying to find a box suitable for a tv is a lot of hassle. The original box is the one that should be used.
Keeping the box for everything is always a good idea. It may not add value but it might make the difference between making a sale or not. It's also useful for packing a piece of kit you have to return for service or repair - having the original box tells the retailer/manufacturer you take care of your gear and MAY encourage them to do the same while it's passing through their hands.