You just spent $$ on Good to Very Good copy of a book because it bears a signature of some dead guy you admire. No, you didn’t get a F/F with an florid inscription because you can’t afford $$$$, but you are very happy with your $$ VG/ndj.
Now what do you do with your new baby? You could put a dust jacket cover on a book that has no dust jacket – well technically it’s just a sheet of polyester without a lining, and that has to be creased JUST so, in order for it to cover your book snuggly. But then it becomes just a shiny naked book on your shelf and the odds are very good the spine can’t be read from a distance. So, all those friends you want to impress, when you whip it off the shelf and say “look at this!” are just gonna screw up their noses and say, yeah but it’s ugly.
For about $22 bucks you can usually get a spiffy reproduction of the dust jacket, clearly but subtly labeled facsimile, to wrap around your prize. It will then do what a dust jacket is supposed to: protect your book from the dust in the air, the light coming through the window and various and sundry other possible household dangers. It also proclaims from a distance the title of your prize possession. And for good measure you can slap a dust jacket condom over it.
Maybe it’s just me, but fake jacket or not – I think a naked book feels better when it’s dressed.