Why should you exfoliate?
It's always good to get rid of dead skin cells. They can clog pores and the cause dull looking skin. By eliminating dead skin cells, your skin will be able to absorb serums better.
Exfoliating should happen up to 2-4 times each month, and make sure to moisturize your skin afterward.
Type of exfoliants:
Scrubs: These are the ones that physically remove the dead skin cells. The size of particles ranges from large to micro exfoliants.
Chemicals: These types contain alpha-hydroxy acids (aka AHAs which are found in fruits) and dissolve skin. They also go down deeper into skin layers whereas scrubs just physically exfoliates, an outer layer only.
Enzymes: No scrubbing necessary, these melts away the dead skin cells. Similar to chemical exfoliants but not containing AHAs. Typically, they'll have enzymes from pineapples or papayas.
Which one should you use?
It really depends on your skin type. For an example, if you have a very oily forehead and cheeks, it's best to use two different kinds of exfoliants for each part.
Scrubs: Scrubs are good for oily skin because they'll lift off the oil and dirt and other impurities. Scrub gently because you wouldn't want the exfoliants to damage your skin and break down collagen. Even though they are known to get you better complexion, stay away from scrubs because they are less likely to do good (ex. environmental wise).
Chemicals: A good option for dry skin. Dry skin has a tendency to sag faster and this will help your skin to be firm.
Enzymes: A good option for sensitive skin because it doesn't include scrubbing nor AHAs.