There is a lot of debate about how often MPs should vote differently from their party leader in Parliament. There are many free votes, where party leaders officially give permission for MPs to vote the way they think is right, and some MPs sometimes do it even without permission. But most of what MPs do is things other than voting. They represent their constituents a hundred different ways, in committees improving laws, presenting petitions, presenting the written questions that the media ignore, pushing projects, and representing the interests of individual constituents and groups before government officials high and low.
Whether people vote for the person or for the party at election time or for a combination of the two, the MP needs a credible personal mandate from his or her constituents, regardless of their party’s mandate, in order to represent you effectively.
When an MP is representing you, for instance arguing for a local Employment Insurance rule or for protecting a natural area, an official might think “only 35% of voters in that district voted for this person. Maybe most residents disagree.” That MP has a weak personal mandate. When he or she speaks, there is a suspicion that people might very well want the opposite.
A ranked ballot ensures that MPs have a strong personal mandate. They can only win if more than 50% of voters give them this mandate. With over 50% there is no doubt that their constituents gave them a mandate to represent them. Whether you prefer MPs who follow the party line or MPs who are more independent-minded, your MP needs a strong personal mandate of over 50%. A ranked ballot is the best way to do that.