1. The dolls!
I have mostly BJD, and they solve a frustration I'd had since early childhood...realistic posing! I have no idea why the posing limitations always bothered me, but they did, and my Fairyland dolls are pretty much perfect. :D
There's such variety, and even the same sculpt, with the same faceup, usually looks very different from one owner to the next. It is endlessly fascinating to me...
2. I get to use a whole bunch of other hobbies in conjunction with this one.
I love knitting, and sewing, and crafting in general... I can use a lot of these skills to make things for my dolls, and while I'm no expert at any craft, my skills have vastly improved since I started making things for the dolls. I mean, I did a dress with a lace skirt the other week! Lace! A couple years ago, I would have probably just assumed it was too hard.
I've learned tons about how clothing is put together and how to make something without a pattern when necessary. I still prefer using patterns, but I feel like I can at least try to come up with something when I can't find a pattern these days!
And photography....my family and friends tend to dislike pictures of themselves once they hit about 10, so they become reluctant to pose! The dolls are always happy to pose (and so cooperative about it, too!), and there are people who are amused enough to look at them for fun.
3. The people!
It's lovely to have like-minded people who get excited over a new doll, outfit, photoshoot, or a wig! And my Flickr friends, blogs I read, and DoA are a constant source of inspiration and admiration. There are so many people doing such awesome things with their dolls, and it always makes me want to learn more!
It's also been good for me...I'm not good at New People. I worry that I might be bothering people or intruding, but I'm much braver about commenting. Okay, yes, I still dither over every comment I leave, no matter how inoffensive, but I do leave comments! LOL
While there are always a few bad apples, the people I've come across in this hobby have been a higher than average concentration of very kind and generous people. I love that. :)