See that the sole lining has some contouring to accommodate the arch of your foot (arch-supports).
See that the side lining has some contouring to accommodate the arch of your foot (arch-supports).
Highlighting and contouring will add the 3-D appearance back to your face; one shade of foundation all over can give your face a flat, lifeless look.
You may want to save highlighting and contouring for special occasions or days when you just have more time to get ready, especially if your foundation coverage isn't very heavy.
Light and medium coverage foundations are less likely to mask your features, though highlighting and contouring can look beautiful on top of those formulas as well.