The primary advantages of the pick are its speed, its ease of striking large chords and, because the fingernails and fingertips are not involved, its preservation of player's picking hand. Furthermore, use of a pick makes a louder and brighter sound. Its primary disadvantage is its imprecision, making muting strings necessary. Also, if the player wishes to switch to the tapping style, he or she can tap with or with out the pick: to tap with the pick just put it on its side and tap it on the desired fret. However, tapping with a pick makes it harder to tap on multiple strings.
Players wishing not to use a pick may try finger strumming. This is accomplished by holding the picking hand's first finger to the thumb, much as one might hold a pick, and striking the strings with the first fingernail. Anything in this book written for a pick can just as easily be played by finger strumming.
Content Credit: http://en.wikibooks.org/wiki/Guitar/