In practice, the extract centroid is useful for a variety of transform functions, RBD simulations, and more.

Run over:

--  Pieces = By default, this node will run over all the pieces of geometry that are defined by a piece attribute.  If you don't have a piece attribute, then this node will error out.  So, you can fix that by setting down a connectivity SOP and making an attribute that assigns a unique ID to each piece of disconnected geometry.

--  Primitive = This will take a look at each primitive (usually that means each polygon of a mesh) and generate a point for the center bbox or center of mass

--  Detail =  This will find the center of mass or bbox for the entire stream of geometry that is being plugged into this node.

Piece Attribute:

--  This is asking you for the attribute name to look at when the "Run Over" is set to "Pieces."

Method:

--  Center of mass = This looks at the shape of your object and favors areas which feature more area over areas that do not.

--  Bounding Box Center = This draws a box over the geometry and outputs a point in the center of that box.

Output:

--  You can either output points or store this information as an attribute.

Transfer Attributes:

--  This allows you to transfer any point attributes from the mesh to the newly generated points

Transfer Groups:

-- This allows you to transfer any groups from the mesh to the newly generated points