In instrumental music, if there is a prgression of like metered notes, for instance, 2 eighth notes, or 4 sixteenth notes, they will almost ALWAYS be joined with a beam. This is NOT so sheet music with a vocal line. Beamed notes in a vocal line means that they are to be sung smoothly (legato), while unbeamed notes are more separated...not as sharply accented as staccato would be, but just separate enough to form a contrast between it and the legato. For instance, if you've ever heard Massanet's "Meditation" with the melody line sung by the human voice (usually a soprano), that would be beamed, while something like hocket would be unbeamed.

--Matt