According to the FDA, sunscreens are vital and useful tool in protecting the skin:
Cumulative exposure to the sun may lead to premature aging of the skin and skin cancer. Liberal and regular use of sunscreen will help reduce the chance of premature aging of the skin and skin cancer in the area where applied. Scars and or brown spots are especially vulnerable to sun damage and can further discolor with sun exposure, so protect yourself with a moisturizing foundation and concealer stick with SPF35.
To achieve maximum SPF potential, sunscreen should be applied at least 30 minutes before exposure, as it takes this long for the sunscreen to take effect.