Single Preference Voting (a.k.a. Plurality Voting)
This is the voting method everybody is familiar with: the voter just selects the option he/she likes the most. The final result is computed according to the number of votes received for each candidate and the results are displayed in terms of percentages.
The single preference voting method is clear, simple and easy to grasp: it is the best method when you need to decide between two candidates. However, in the case of decisions involving three or more candidates, it is unfair with respect to minority candidates.
The problem is that votes given to minority candidates are “wasted”, so people tend to vote the “lesser of two evils” between the first two major candidates. In the case of political elections, the usage of single-preference voting naturally leads to a two-party system (Duverger's Law) i.e. a duopoly regime. In the case of a decision making process this is less of an issue, but still one has the same undesirable effect: when there are two options, which are clearly favourites it becomes counter-productive to vote minority options and people are encouraged to vote insincerely.
Single-preference voting severely restricts the voter's expressiveness.
Since the voter is forced to select just one candidate between many, he/she has no way to express the fact that he/she equally likes two or more candidates. Also, he/she cannot express the order of his/her preferences. If you have many options to choose from and want to give more freedom to your electors, it is best if you switch to a multiple choice voting method.