I'm not big on music, movie or gaming piracy, so I'm not going to tell you all the benefits of an R4 card for your Nintendo DS, DSi, Lite, XL or 3DS so you can go and steal products online.
I bought an R4 card a few months ago so I could have extra storage on my DSi XL, I wanted to be able to store things on it for when I was traveling long distance.
I've got a 32GB card and I've almost filled it with movies, music, photos, ebooks, and games that I've downloaded from the Nintendo store (some of them for free!), and they're all saved securely on that one little card.
It makes life so much easier, rather than carrying around loads of games, an mp3 player, books, DVDs and even a portable DVD player or a laptop! Nope, just me and my DS!
Photo: abusx (Flickr)