I have 3 copies so far and am looking into getting a fourth.
Short answer: I have too many dreamies and I want to help people.
Long answer: I ended up garnering far more dreamies than I'd ever anticipated, with practically half of them being normals. I'm not good at picking favorites, nor am I good at allowing change or letting things go, so I needed at least two.
Then that turned to three. That third was supposed to be my cycle town until I got smacked in the face with more dreamies.
And now I'm eyeing a fourth copy and a second 3DS. I want to finish up the dreamies and FINALLY start helping people ;-; It's so stressful haha. But, perhaps I'm not meant to help anymore than I already do. Four is quite a lot. ]:
I have a second copy, but not because I wanted one. I picked up a used New Leaf 3DS XL from Gamestop, and since the system had been formatted, I didn't expect it to include New Leaf. However, when I went to the eShop after doing the system transfer, it let me download NL for free, even though I had never downloaded it before. I originally used that town for cycling, but I don't cycle anymore.
I had a 3DS and got an XL. I decided to have a copy for both machines, mainly because I was after the streetpass items at the time and was having a hard time getting them by streetpassing people. Besides that, I figured my second town would be a place to farm animals to swap over to my original town. As I started to develop my second town, it became even better than my original. And, I turned off streetpass long ago because I didn't want to pick up my own animals when I got down to 9 in either town, and I haven't missed it. The streetpass items were really starting to flood my inventory, with the two machines constantly streetpassing each other.
I actually ended up not liking the XL and bought a third regular 3DS with the intention of selling the XL. I haven't done it yet, so I have a third town. It's not a bad town, but I don't have time to play three regularly. I have sent a few animals from that town to my second town.
My first town is essentially done. In fact, over the last month I wanted to make some cast switches with the villagers. Keepers are originals Jambette, Scoot, and Twiggy. Drago, an early move-in, must stay. But it was my evaluation and re-evaluation of others that had me thinking: 1) I should have personality types; 2) Since my town of Applewin is essentially done, I don't need to have myself covered with the personality types. (The eight categories of personality types are normally essential to accessing suggested Public Works Projects.)
I have a second town to help with turnips; to help with a different identity of a town. (For example, in Applewin I have for my Train Station and Town Hall Fairy-Tale; in Progress, I have for my Train Station and Town Hall Zen.) Instead of being limited to 10 villagers, I have 10 more in a second town. (I don't repeat a villager.) And I can figure who should be in which town. (I'm going to work on switching Broffina from Applewin to Progress; and to switch Tia from Progress to Applewin.)
Given my first town is essentially done (cosmetics can be switched up here and there; I do need gold roses, black cosmos, and purple tulips), I can take time to build the second town further. The maps are very different. In Applewin, the beach is to the east as the Museum is to the west; in Progress, the beach is to the west as the Museum is to the east. The native fruit are different: in Applewin, it's oranges; in Progress, it's peaches.
Having more than one copy of "Animal Crossing: New Leaf" means one really, really, reallyLOVES this game.