In Drupal the output of fields is controlled via "formatters". For example an image field can be output as the full image, as a thumbnail or simple as a linked file path. This setting is usally set per field, but using the field_formatter and field_formatter_preset modules the editor can choose the output format per each field instance.
The field formatter module allows to choose and configure the formatter on the node edit form. If the formatter has a lot of settings, the configuration of the formatter can be quite difficult for the editor. The field_slideshow formatter - for example - allows to render images as a slideshow, and 20+ settings to configure the slideshow. It is not feasible for the editor to configure the slideshow on every node again - but here field_formatter_preset module can help!
This module allows to prepare predefinded formatter configurations for field_formatter. On the node edit form, the editor then only has to choose the preset and not fill out the complete configuration form for the formatter.
Note: Use the dev version of field_formatter to make it work with field_formatter_preset!