It's about delegates count. The primary, caucus elections are all about that. Super Tuesday gets all the attention because of the states where candidates compete have the largest number of delegates that Presidential candidates can win, in order to get the party nomination.
Next Tuesday, March 1, it's an important milestone for the candidates because they're competing in a dozen of states and a territory. Winning these states would not only give them the largest number of delegates but also a measure of electability for the general election in November.
On the Democratic side, Hillary Clinton or Bernie Sanders need to win 2,383 delegates to get the Party nomination. There is a total 4,189 delegates available. A total 1,034 delegates up for grabs from the Super Tuesday states.