If you confirm this, all the history or recent used (searched) folders, text and wildcards will be cleared.
The history is useful to quick selection of most used folders and parameters.
History of parameters are available on "What to search" group. You can right-click on folder's box to get a popup of recent searched folders, and can click on proper button on "String to Search" and "File Mask(s)" (wildcards) to get a list of recent used settings.
Note: the new clean history is not saved until any search is started.