If the author doesn't consent to this mean of distribution, then it is illegal. Whether or not the recipient also owns a copy of it doesn't matter in the slightest: I can't give you my fresh E-SWAT rom, even if we both own a copy of the game.Дownloading is also illegal in this sense: even if morally you could have a point if you own the original cartridge but lack the hardware to dump it, the person who gave you the ROM is distributing it without the consent of the author. What you are not allowed, however, is to give the backup to other people, even for free. Which means, for our ROMs, that you are allowed to make a copy of your stuff and do whatever it pleases you with it: patch, disassembly, wallpaper, anything you want to do for your personal use. A book owner however cannot make copies of it to give or sell to other people, as that is the sole prerogative of the author. As such, a book owner can read it, burn it, shit on it, resell it, without approval of the author. The author have rights over the words in the book, not the book object itself. What people do with the copies they have acquired from them is out of their reach. By their work I mean their original work: their words, their pictures, their data. The author, or the rights owner, is the only person who can decide if, when and how their work is distributed. Copyright laws for the most part regulate how a work can be published or broadcast or distributed. Morally speaking, these are yours and come from a trusted source.

Practically speaking, none in most cases.

Gba exploader r4 2016