The lower the expectations set by the medium, the less friction there is for ideas to be transmitted to it. Example: Moleskine sketchbooks are great, but the premium quality of the binding and the paper present you with a high expectation of what you should do with it. If all I want to do is scribble a quick sketch, the high quality paper is intimidating — it expects to be used for something good, something important. This introduces higher expectations, and thus higher friction to using this tool. On the other hand a cheap sketchbook, a piece of scrap paper or a napkin present no such friction because there are little to no expectations. Whatever you scribble on those is better than nothing.
In the same way this is the tradeoff of reading a paperback book versus a beautiful hardback book. With the paperback there is no resistance to highlighting passages, making notes in the margins or folding paper because the materials are cheap. You can really use a book like that to learn. The well made hardback is a different beast — it gives you the best reading experience but it also expects to be used with respect, so the advantages and the drawbacks are flipped around.
This principle applies to software, too. For example, here’s a great post by Tobias Ahlin about skeuomorphism. Tobias makes a sharp insight on how the Paper app for the iPad uses sketchbooks to reduce the friction of capturing ideas. The interface for managing your sketches are fully animated 3D sketchbooks that you can flip through (with your work visible as you do it). It’s not a gimmick: the interface specifically frames your work as sketches in a book rather than as drawing or paintings on individual canvasses as other apps in the category do. The canvas sets higher expectations for your drawing than a page in a sketchbook, which in turn introduces needless friction.
Reversal: oftentimes we want to reduce friction, as in the case of committing an interesting thought to paper, but other times the higher expectations may serve as a filter. Personal publishing services want to reduce the friction of sharing our thoughts to a minimum so that people can blog or micro-blog their content as much as possible, driving up the rate of their content creation machine and increasing the flow of traffic. This sort of publishing does little to encourage the user to filter their work, to stop and reflect, to evaluate and judge, to select the good from the rest. In this case friction would be good if the aim was to create something of value, to create a healthy sense of self-doubt — not destructive enough to paralyze, but high enough to let only a slow, filtered stream through.
This then can be reduced to two types of friction: one that is a barrier, and one that is a filter. The barrier is the type of friction that stops you from committing your ideas to paper (or the digital canvas). Ideas left aside for later are too likely to be lost and forgotten and so this is the sort of friction we want to remove and avoid. The second type of friction is a filter, and this is what helps us pick out the good from the bad. This sort of friction is healthy when we want to publish something for a public audience for it is through our power of judgement that we put forward our best work.