(This item pertains to the check boxes on the General tab of the Setup Options dialog box. You can open it through the F5 key or through the Edit | Preferences | Setup menu option.)
When you select this check box, you can apply thickness to points created with Point Only Mode. Selecting this check box makes the Thickness box in this same dialog box available for editing. You can then type a thickness and apply that thickness to points created using Point Only Mode.
For additional information, see "Point Only Mode" and "Thickness".