Whenever you are singing fast, energetic songs, the music will sound good if you make small accents on the notes. In this way you are emphasizing the rhythmical character of the music. We might call this ‘percussive’ singing. It is opposite to the classical way of legato singing.
The term ‘legato’ is common in classical music. It indicates that you should bind the notes, preventing gaps between them. But at the same time the term is used to indicate that the notes should keep their volume, creating a continuous sound. We might depict legato like this :