The Oscar-winning actress had worked on some projects where the set was "like summer camp" and everyone got on well, but the end result was an "awful" movie.
Speaking at the Toronto International Film Festival's (TIFF) In Conversation With... series, she told the audience at the Royal Alexandra Theater: "There's a sort of misconception somehow that making a film, when it's great, is like summer camp. I've been on a couple of those, and the films have been f****** awful.
"Polite disagreement, respectful disagreement is super important in the creative process, and know you've got a healthy relationship with someone when you can really fight for things, but then allow your mind to be changed."
Blanchett made her comments as she recalled working on her 2015 drama Carol and urged director Todd Haynes to "step away" from the set to "clear (his) head" during a complicated scene set-up.
She said: "One night we were shooting a scene in Carol, the house was kind of a strange abandoned house we were shooting in that was really hard for Ed (Lachman, cinematographer) to get the light in to light the scene properly. It was really complicated.
"You could tell Todd (Haynes) was finding it really difficult.
"You expect a director to have everything together and hold it together all the time.
"Sometimes they're the ones that need a hug. And you need to say, 'Why don't you step away and clear your head a little bit?' In the way that he'd make the space for the actors to do that, we make space for them."
The 55-year-old actress recalled Haynes agreed with her suggestion and "he stepped away so we could figure out a different way to position it."
The Tar actress insisted "you always want to do the best for a director like that" so that the work can come together in the end.
She added: "It was quite fluid, but there's no conflict with him. He's sort of conflict-averse. That doesn't mean you necessarily have to agree."
One of the Australian actress' "best jobs" was in 1999 thriller The Talented Mr Ripley, which also starred Matt Damon, Jude Law and Gwyneth Paltrow.
She said: "It was one of my best jobs.
"It was such a great — I had the best summer with Philip Seymour Hoffman... we went to a place called Fashion Pizza. We ate lots of pizza. And I got Matt's fabulous apartment because he needed to be in the Four Seasons training every day whereas I got to luxuriate."
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