Allows Parliament to call Government to account if they stray away from their manifesto promises.
Voters can decide at the next election if they feel the government has delivered on their manifesto - voters in 2001 gave Labour their mandate due to approval of their actions.
Helps Parties to maintain discipline as MPs are bound by their party mandate.
Disadvantages of mandates
Mandates rely on one party winning an overall majority - if coalition or minority government then no Party can claim a mandate and government lacks legitimacy.
Mandates are exhaustive and assume that all voters support the Party's manifesto policies.
Circumstances may change after a Party take power, for instance COVID and the Conservatives.
Manifesto commitments can be vague and so calling the government to account based on meeting it's mandate is hard.
Examples of manifestos
2017 Labour Manifesto; 50% income tax for those earning above £123,000; abolish tuition fees; arms sales to Saudi Arabia ended; build 300K homes a year for 5 years.