Object Selection tool

The Object selection tool is essentially more of a guided Select Subject command and should be thought of as offering a way to get a reasonable quick selection. It’s not really meant for refining selections since Photoshop already has other tools for such purposes.
The Object selection tool has a Lasso and a Rectangle marquee mode. The marquee mode for example, simplifies the process of selecting a single subject, or part of a subject, by allowing you to simply click and drag a rectangle around the object.

The Auto Enhance option in the Toolbar works better on things like hair to produce soft-edge selections. If this is checked when selecting sharp edge subjects you may get halos around your selected object. When the Object Subtract option is checked, you can subtract from an initial selection with the Alt key held down to auto calculate the subtraction area. Figure 1 shows (top) a modified subtract selection using the Rectangle marquee. And, below, a modified selection using the Rectangle marquee, but with the Object Subtract option checked.

Figure 1 A comparison of a subtract selection with the Subtract Selection option unchecked (top) and checked (below).

The Object Selection tool in use