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.