Analytics processing component in Search for SP2013 requires additional 300 GB disk space (apart from 80 GB for the other search components hosted on the server except Index component) for local processing of analytics data before it is written to the analytics reporting database. Also it is preferred to have it in a separate disk volume or partition.
If you want to change the default location then you will have to set the data path on install. The UI text is a bit misleading as the location is for all search data files not only index files. The index file location however can be changed even after SharePoint is installed using PS scripts.
While the index can be moved, i have not found a way to actually move the analytics processing location.
NJF - That's right. We will have to set the location of analytics processing data during installation; once it is set at least as of now there is no PS/Object model code available to move them again.