The Settings tab in Filter Controls displays filter-specific controls (created by control components), global parameters (Size, Variation and Seamless Tiling) and the Randomizer:

The first section (above the separator) shows the filter controls which are specific to the current filter. These controls are created in the Filter Editor using the control components. The order of these controls in the list can be modified in the Order of Controls dialog.
The second section (below the separator) shows global parameters which are common for all filters:
In certain situations, some of these parameters may be unavailable – for example, if a filter uses no randomizable components, the Variation slider will be disabled. Similarly, the Size slider is disabled for filters that don't require any measurable distances.
The last section is called the Randomizer. It allows to randomize some or all of the controls in the two previous groups and on the Lighting tab. The Next Variant button generates a new random set of settings, and the Back button reverts them to the previous state, acting as a local Undo function. The Randomizer can be configured using the Randomizer Settings which are accessible by clicking the
button located right next to the other two Randomizer buttons. When using the Randomizer, you may also reduce the preview size by choosing View > Preview Size > Reduced from the menu to get the results quicker.