The single party system is characterized with continuity, which means that the upper level party members are rewarded with privileges. The disadvantage of this system is that there are no no choices.
In the two party system when dissatisfied you can vote for the other party. There is also stability and continuity, but the disadvantage is the stifles view of minority.
The multiparty system provides voters with more choices and there is a broader political spectrum represented. However, in this type of system it is difficult to win a majority, plurality and that is why coalitions must be formed.