I want to explore one of his points a bit more, though. He talks about the idea that “grids can impede creativity.” That’s false, for sure, but I think it's particularly important why it's false. Ellen Lupton (who he quotes) puts it this way: “To say a grid is limiting is to say that language is limiting, or typography is limiting.”
All of these things are, indeed, limiting. But they are limiting in helpful ways. We observe rules of language because, having agreed upon them ahead of time, they help us ensure we are not misunderstood. The rules of typography have been developed over centuries of printing (and calligraphy) to aid the human eye in clearly reading and interpreting letters on a page.
That's not to say no one breaks the rules (of either English or typography). But to do it effectively requires extreme skill, because you’re working without a net. A master writer may violate a point of grammar or use a word incorrectly because it lets her tease more meaning out of it, rather than less; a great typographer may set text with intentionally irregular spacing or on top of itself or other lines to achieve an effect. But for most people, and in most cases, it is better to follow the rules.
So it is with grids. A grid system is extremely flexible, but it provides constraints that promote good design. It encourages hierarchies and prioritization of content, standard sizing of elements, and a good, clear flow to the work. To the extent that a grid limits you, it mostly prevents you from doing bad things. The grid frees you to be creative without having to worry as much about those things. That's an unalloyed good.