I don't have a long arm but I'm shopping around for a used one. I've been quilting ten years and it's pretty much taken over my life. It IS my life. I don't think it's a necessary thing - just like a lot of sewing doodads and gadgets. I know that I have always been artistic and am really passionate about my quilts...I am totally capable of quilting large quilts on a domestic but I just don't really want to. I think to own or not own a long arm is a really personal choice and it's hard to judge someone else's reason for wanting one.
I'd like to make a little money on the side with mine because quilting is my passion but we are on a tight budget...if I didn't currently do commissioned projects or sell on Etsy I couldn't have afforded half of the things that I have for my sewing. But I'm not planning on running a huge business any time soon. I think when you start quilting hundred of quilts you lose time for yourself and your own creativity and I know for me - I don't want that. But I can totally understand why someone would. (I have small children at home - I'd like to make a career of my quilting some day in some way, but for now they are my priority over all other things.) It was a HUGE decision to set aside the money for this purchase, I have never spent this kind of money on myself. The most expensive thing I own other than my house or my car is a $300 featherweight! Lol* I don't think I would either if I weren't absolutely sure I would use it. It's not for everyone - and if you are an avid quilter who'd like more space there are a lot of other options aside from a long arm.