The Dash in the Ubuntu desktop shows results of documents, music, videos, spreadsheets and other files that match the search string. I find that this slows down the Dash, since I use it only to search for applications.
To disable one, a few or all of the different types of files that Dash searches for, is easy. Go to System Settings > Security and Privacy and in the tab Files and Applications choose which files you want searched for or just disable it completely.
Tried with: Ubuntu 14.04