When we talk about trade-offs in Parliament, we're talking about what kind of parliament we want. Electoral systems produce a Parliament, and a Parliament looks a certain way based on the electoral system.
Imagine the electoral system as an engine. Depending on how you tune that engine or what kind of engine you have, you're going to get different results. It's really about the principles that guide you. Effectiveness is a great concept, but when we talk about effectiveness, we can talk about effectiveness being a large majority government. One would not disagree that a large majority government is very effective in getting legislation passed, but it sacrifices the effectiveness of Parliament, which is after all a talking place, and the ability of members on all sides to engage in discussion and to deliberate.
When we talk about effective parties, we can talk about large brokerage parties that command wide swaths of ideology as they do in Canada, or we can talk about effective parties as being small, regional, or specifics-based parties. The trade-offs are really around the kind of Parliament you want and the kind of government you want.