As Johan mentioned, the styles you can select for TemplateGrid are a few default styles for showing data in the grid in different combinations.
Generally speaking, TemplateGrids are used for displaying data in a more-or-less arbitrary form, in an x-by-y grid. DataGrid uses '1 object per row' approach familiar to anyone who has used a spreadsheet. TemplateGrid gives you more freedom (plus the ability to use images other than icons, MicroFlow triggers, etc). The price for this is that you can't dynamically sort on attribute columns (as they don't exist in a TemplateGrid), you can't do inline-editing and you don't have aggregate attribute columns (because, again, they don't exist).
What you can do, however, is change the CSS class of a TemplateGrid. If you're working with (or are yourself) a designer, you can define the CSS properties of this grid in a theme package and make it look any way you want.
This makes TemplateGrid well suited to styling grids with photo albums, shopping products, inventory items, etc.
The styles you can select in the Modeler for a TemplateGrid are just a starting point.
These are the default styles / themes for the TemplateGrid to show some possibilities. Just try them!
Input about changing these default styles is welcome (the styles are not really representative for what is possible with the TemplateGrid)!
It can safe a lot of time if default forms and grids can be generated. Is it also possible, for instance, that a dataview or datagrid in which you bring an object automatelically contains the attributes (in a grid presented in the columns)? You can then delete the attributes you don't want instead that you have to bring them in one by one. (maybe a nice feature request?)