I've written about Captivate's Cache folder in the past. In case you aren't familiar with it, a cached version of your project is created in the Cache folder every time you save your Captivate project. The cached projects can make the process of opening, saving and working on a project faster than what one experienced with older versions of Captivate. However, with Captivate 8, developers are complaining about the increased size of the Cache folder.
Those folks aren't imagining things. It looks like Captivate is creating more folders of each project than before. Adobe is aware of the problem and you can expect an update to Captivate that will fix the issue. In the meantime, you should manually backup your projects (to an external drive) and clear the Cache folder at least once a month (by clicking the Clear Cache button).