"Speed is simplicity" is a design law, postulated by the MIT design guru John Maeda in his book "The Laws of Simplicity".
The basic idea is a simple observation: If something can be done quickly, it is positively perceived as simple. And simplicity is assumed to be a (maybe even the most important) design goal.
Examples:
- Wikis are attractive for people because you can change a web page and publish something on the internet in seconds.
- This becomes particularly attractive if such "quick and dirty" contributions accumulate in a way that supports subsequent refactoring, creating a substantial body of work.