I used to do that too, until I discovered
this.
Dropbox is great, but like many people, I don't like putting my documents on the cloud. I also try to avoid write operations on my device if possible. I bought a 64GB SDXC class 10 card on eBay for about $75 that holds all of my iTunes media, handles my downloads, and keeps my Xcode project files for my 13" MBA. Even if I utilized cloud storage, I prefer not to keep my iTunes media on the local SSD.
Th SDXC slot is great not just for moving around documents from machine to machine, but it's the only practical way at the moment to upgrade the storage on the MBA's. Paying $700+ to go from 256GB to 340GB is too rich for many people. But $70-$120 for an extra 64GB SDXC card (or more for up to 128GB) for document/media storage is a great deal in comparison.