It has been said that politics is the art of honourable compromise. Essentially, the mixed member proportional (MMP) system alters how that compromise is achieved.
Under the current first-past-the-post system, political parties must develop a party platform that has appeal to a large number of voters across the many regions of the province. Support in only one region, no matter how high, will help the party elect Members of Provincial Parliament (MPPs) but they will not elect enough MPPs to form the government. Support in all regions but without a large number of voters in any one of them will not elect a single MPP. So, using the art of honourable compromise, parties develop a platform that can attract a large number of voters across many regions.
Under the MMP system, there is a shift in how this compromise occurs so that more of it happens in the legislature. Because 90 of the MPPs are elected on a first-past-the-post system, the major political parties will still need to practice the art of compromise in developing their party platforms.
With 39 additional MPPs selected from lists created by the political parties, parties with a small base of support will not need to broaden that base of support in order to elect MPPs. If a party can appeal to three percent of voters in an election then they will get three percent of the MPPs, even if they cannot garner enough votes to elect one local candidate. This will happen because MPPs will be added to the legislature from the list submitted by that party. So a smaller party can elect MPPs by appealing only to a concentrated base, with that concentration either being geographic or issue based. Under the current system, political parties with such small appeal would not elect MPPs.
That does not mean the end of compromise, however. If no party can form a majority government, which is more likely in the MMP system, then they will need to practice the art of compromise in gaining the confidence of a majority of the MPPs. That is, they will need to seek out alliances with other parties, big or small, so that combined they will have a majority.