Cache
In most use-cases this is not recommended, however if there is high traffic expected, or a lot of repetitive queries, it can be very beneficial.
File - The queries are saved within files in the WordPress uploads directory (within asp_upload).
Database - The queries are saved as options within the wp_options table
This option is recommended, when only large sizes of the result preview images are available on the server (no thumbnails or smaller version).
When enabled, the plugin tries to crop the images from the live results, to be stored in the WordPress uploads directory for further use. It may slow down the search initially (while the images being created), but then it should be much faster - saving bandwith and increasing image loading speed.