I use Dropbox to sync files across my Macs, but also to collaborate with others using shared folders. One day, I discovered that the disk space on my MacBook Air had dropped substantially. I started poking around, looking for swap files and other usual suspects, but eventually found one especially large folder hidden inside my Dropbox folder: .dropbox.cache.
Looking inside this folder, I found that it contained three dated folders, one each for the past three days. Inside each of those were a number of files; many, I could tell, were from my shared project folders. Because we use a versioning system on one of those projects, I could see multiple versions of many files. In all, I found 8 GB of cached files.
On a desktop Mac, that many files wouldn't be a big deal. But if you have a MacBook Air, in particular, without a lot of disk space to spare, it could be an issue. So, if you see yourself running out of room on your hard drive, check that folder and delete files that you know you don't need.
To do so, you need to be able to see hidden files. If that option isn't already turned on, open Terminal and enter the command
defaults write com.apple.Finder AppleShowAllFiles YES. That done, restart the Finder, either by issuing the command
killall Finder in Terminal or by holding down the Option key as you Control- or right-click on the Finder icon in the Dock and selecting Relaunch Finder from that contextual menu. To hide those files again, enter the command
defaults write com.apple.Finder AppleShowAllFiles NO and again relaunch the Finder.