When you operate on a PrincipleOfFirstTrust and AssumeGoodFaith, you are able to go faster and make more progress. Consensus (WhatIsaConsensus) can be achieved far faster. Even when disagreements happen, they can exist without degenerating into fights (assuming good faith makes it easier to AgreeToDisagree, if you have to). Everyday wiki usage hinges on the good faith implicit in the GentlemensAgreement? at the core of the WikiWay. Wiki:RefactoringWikiPages would be vastly inhibited without the assumption of good faith, as suspicion and personal politics would run riot.
Yet good faith has its downside. It is the good faith of a community that trolls (WhatIsaTroll), vandals, FlameWarriors and UnwelcomeVisitors in general exploit to cause trouble; and a community whose participants act exclusively in good faith can still be subject to the TragedyOfTheCommons. Good faith may also be misapplied; it has been [pointed out for a long time] that "the road to Hell is paved with good intentions".
See also: WhatIsTrust
Apologies for this ShallowPage, but the phrase "good faith" appears on Meatball so much that the idea started floating around in my mind, so I wanted to make a start on a page for it, even if fuzzy. -- EarleMartin