While coffee has enormous health benefits (reducing diabetes, Parkinson's, heart disease, and cancer), there's some controversy over how it affects creativity. Some scientists believe coffee reduces creativity, according to an article by Maria Konnikova in The New Yorker:
"Creative insights and imaginative solutions often occur when we stop working on a particular problem and let our mind move on to something unrelated [but] caffeine prevents our focus from becoming too diffuse; it instead hones our attention in a hyper-vigilant fashion."
In other words, caffeine keeps your mind from wandering, which is part of the creative process. The problem with this theory is that it may overestimate the importance of free association (i.e. mind wandering) in the creative process.
Here's the thing: insights are pretty much dime-a-dozen. For example, friends, colleagues and I myself have hundreds of times come up with crazy brilliant ideas for businesses or new content... all of which went exactly nowhere because none of us had the time or energy to develop those ideas.
Beyond an initial one-line concept statement, the creative process isn't so much a series of original insights but the ability to make small creative decisions, like how to word something, what flake of stone to chip, or what paint color will works best. As Thomas Edison's famously pointed out: "genius is 1 percent inspiration and 99 percent perspiration."
When you're actually executing a creative vision, that is, doing the hard work required to manifest it, big new insights are a huge distraction. So called "creatives" who are forever generating new ideas typically have a CV with two types of projects: 1) unfinished and 2) un-started.
Which is exactly where coffee comes in.
Coffee is enormously helpful to the creative process because it suppresses unwanted and unnecessary insights and instead helps you focus on the work at hand. It helps you get down to work, stay on the project, and make day-to-day progress, rather than daydreaming up new things that you might be doing instead.
Like mindfulness meditation, coffee helps you block out your "monkey brain" which is constantly jabbering every which way and instead listen to your "ox brain" which thinks about one thing at a time--which is exactly what you need to get the work done. As one prolific author put it: "Writing is the process of turning coffee into ink."
To be more creative, then, you should schedule times--like commuting, housecleaning, or hiking--where your mind can just wander... but then don't drink any coffee either during or beforehand. That's when you get for the insights you need that don't come when you're focusing on the work.
However, when you sit down to actually execute your vision and turn your insights into reality, drink coffee and plenty of it.