The Auto Categorization toggle lets you pick additional Categories that will automatically be applied to all objects placed thereafter. This speeds up the workflow by omitting the extra steps needed to assign relevant categories post-insert for each and every object.

The Auto Categorization tool is accessed from the top right of the top bar. 

It has 2 states:

        Disabled             Enabled

When the tool is enabled, a drop-down menu appears under the icon. Here, you can check the box(es) for which Category (or Categories) you would like to apply to the objects being placed. This Category will be applied in addition to the default Categories for the object. 

This list will show all standard, extension-related, and custom Categories present in the Categorization dialog box.

At the bottom of the menu, you'll see the following icons:

                             Opens the Categorization dialog.

          Expands all / Collapses all sub-categories in the drop-down menu.

                             Resets or unchecks all Categories in the drop-down menu.

                             Opens a Help dialog.

Inserting or placing objects with Auto Categorization enabled

When enabled, placing an object will prompt a toolbar at the bottom of your active 2D/3D view.

This toolbar will display both the default and additional Categories that will be applied to the objects being placed. If you don't check any additional boxes in the tool, this toolbar will display the default Categories being applied. These default Categories will show highlighted in grey. 

               Default                        Additional

You can also temporarily apply additional Categories from this toolbar. While placing an object, before clicking the object in place, click on the Categories icon. This will display the full list of Categories with any selected in the tool from the top bar shown in grey. Check the boxes for the ones you wish to add then click to place the object. The additional Categories will be deactivated once you press the Esc key or move the cursor off the drawing area to release the active object.

While placing an object, you can also remove a Category that is being manually added in the tool. To do so, hover over the category in the tool bar and click the red X that appears. This will remove that Category from just the object being placed at the time. The Categories will divert back to the selections made in the tool from top tool bar with any object thereafter. Default Categories and Categories being applied by a View Mode cannot be removed.  Although there is no default shortcut for this tool, you can assign one in Keyboard Shortcuts in the Tools group.