How important is a "full set" for low price watches?

[arthurl]

Very often, we see want to buy or offers to sell with the "full set" term attached.
And the price magically goes up!
If its an expensive piece, I can understand but for watches that cost just a few hundred, how important can a box or card be? Except the warranty card if watch is still under guarantee can save U some money in case it needs attention.
What are your views?

[Peg308sw]

lol

[KazeKei]

A few hundred $ watch should not really matter if it comes with or without box/paper, the value will be affected yes, but shouldn't be more than 50$