Tab is good for beginners that don't know how to read sheet music, or for people who need a visual representation of what to do.
(sorry for the absence of pictures, the illustrations are included in the text itself.
Step 1: What Exactly is Tab?
1. Music . any of various systems of music notation using letters, numbers, or other signs to indicate the strings, frets, keys, etc., to be played.
Tablature is a "true representation" way of showing you what fret and string to press. I find it very easy to read, and would prefer it anyday over sheet music. One disadvantage of tab is that it doesn's show you the beat or timing of the music. Many guitar music books contain both for just that reason.