Scotland and New Zealand still hold by-elections, despite having adopted the additional member system, in which members are also chosen by party lists. The Republic of Ireland holds by-elections despite electing members in multi-member constituencies by the single transferable vote.
Alternatives to holding a by-election include recounting the original votes while disregarding the candidate who has withdrawn as in Tasmania or the Australian Capital Territory, keeping the seat vacant until the next general election or nominating another candidate with the same affiliation as the one whose seat has become vacant – typically, in list systems, the next candidate on the party list.
However, by-elections can become crucial when the ruling party has only a small margin. In parliamentary systems, party discipline is strong enough so that the one common scenario for a vote of no confidence to occur is after the governing party loses enough by-elections to become a minority government. A UK example was the Labour government of James Callaghan 1976-79.
By-elections can also be important if a minority party needs to gain one or more seats in order to gain official party status or the balance of power in a minority or coalition situation. For example, Andrea Horwath's win in an Ontario provincial by-election in 2004 allowed the Ontario NDP to regain official party status with important results in terms of parliamentary privileges and funding.
By-elections may occur singly, or in small bunches, especially if the authority responsible for calling them has discretion over the timing and can procrastinate. They are sometimes bunched to save money as holding multiple by-elections is likely to cost more than holding a by-election to fill the vacancies all at once. In Canada, in 1978, 15 by-elections were held on a single date, restoring the House of Commons to 264 members. The media called it a "mini-election", a test of the Liberal government's popularity with a general election due in less than a year. The 15 districts stretched from Newfoundland to British Columbia, and produced some unexpected results, for example, an NDP candidate winning in Newfoundland for the first time.
Party leaders and media commentators often point to by-election victories as important signals, but very often by-elections hinge far more on local issues and the charisma of the candidates (especially under single-seat constituency systems) than on national issues or how the voters feel about the governing party. Nonetheless it can be shown historically that a main opposition party which performs consistently poorly in by-elections is unlikely to be a serious contender for power at the subsequent general election.