Botox is used to reduced over movement in high expression areas. This allows your collagen ample time to "fill" in the fine lines/wrinkles.
 
Average units/area:
Between brows- 20 units
Forehead-12 units
Around eyes- 24 units total
Massetters- 24 units total
Lip flip- 10-20 units
Neck bands- 20 units
Jawline lift- 20 units
Underarm sweating- 100 units