Here’s an experiment to try:
(1) Standing still, put one foot in front of the other (as if you were taking a single step), then shift your weight from one foot to the other. You should feel pretty balanced.
(2) Now try the same thing with your feet side by side, hip distance part, and you should still feel balanced.
(3) Now, from this same position as in #2, move one foot forward and try it again. This time, you should NOT feel balanced.
If either you and/or your social dance partner are/is not experienced, please keep this in when when you are dancing (or leading) a box step in any dance. If you step forward/back, then side-together WITHOUT first brushing your free foot forward/back alongside the weighted foot, you are putting yourself and/or your partner into a position of temporary imbalance.