The occurrence records in the Atlas are points.
Admitted, the accuracy of the location can often mean that the species was seen within a defined area, but the Atlas can only treat it primarily as a point, with an uncertainty radius if that information is available (see coordinateUncertaintyInMeters). There are three other types of species data (checklist areas, expert distribution polygons and prediction areas) that indicate where a species is likely to be found. Points to grid transforms a point to an area.
Points to grid also optionally generates occurrence data into a sites by species data matrix. This table is effectively a series of area checklists - what species are in what grid cells. Sites in this tool mean grid squares. The output from the tool is therefore a matrix of user-defined sized grid cells by species. Usually, the species in question will be a species group such as Eucalyptus, lifeforms such as amphibians but can be as generic a List as you like.
As a side-product of this tool, you can optionally generate a species richness and an occurrence density map. Could be handy. Could be illuminating?
More information about this option can be found at Tools | Points to grid.