This is a weird option. It arises because for some odd reason, Windows allows edit boxes to be independently scalable, but not combo boxes, whose size is based on the font associated with it. If you have a mixture of combo boxes and edit boxes on a screen, you may find that it looks bad for them to be different sizes, as in the following excerpt:

If so, check this option, which will force the edit box height to conform to the combo box height as shown here:

Note that this will defeat the ability to scale the combo box height by increasing the window height. But you should be able to adjust the height of these controls by changing your font scaling factor.