If you keep your watches wound when you are not wearing them, they will experience unneccessary wear and tear. One of the hardest things on manual wind watches is the winding of the crown.
If you have a watch with a 56 hour power reserve and you wind it at the same time every day then you will be operating the watch in the same segment of the mainspring so it seems that this should produce a more consistent functioning from day to day nada fully wound watch is generally more accurate, so your watch repair shop's advice is probably correct in that regard. However I would have to disagree that they will "last longer". My feeling is that the less often you wind them the less wear and tear on the watch and the longer your interval between servicing can be.