Moderate exposure to sunlight is absolutely essential to all life on earth. There are various reasons, both biological and psychological, why exposure to sunlight is desirable. In addition many people believe  they look and feel better with a tan. Therefore having a tan may provide a psychological and biological uplift.

UV-B rays are the main source for Vitamin D for our bodies, which helps to promote healthy bones and the absorbtion of calcium and phospherous in the body. Studies suggest that this vitamin is linked to the prevention of breast, colon, prostate and ovarian cancers. It may also reduce the risk of heart disease,  it may increase the metabolism and  treats seasonal affective disorder (Winter Blues)  or depression especially in the winter months when sunlight is lacking.

Absolutely, building a base tan before going on vacation will ultimately prevent you from burning under the hot rays of the sun.  It is still essential to wear sunscreen when outdoors, but having a base will make the process more gradual. It normally would require 4-5 sessions to develop a desirable base.