On the SitePoint PHP blog they've posted a tutorial about the Theory of Constraints, how it can be related back to PHP and what it means for building effective code.

I had been reading The Phoenix Project, a great novel about IT (you read that right), which presents day to day IT and devops problems at a large Amazon-like company in a way which makes mortals understand the complexities and chaos of 21st century technology.

Without giving away any spoilers, at one point in the book the Theory of Constraints is mentioned. [...] The Theory of Constraints can be distilled to the idea that the chain is only as strong as its weakest link.

In the book it was phrased thusly: "Any improvements made anywhere besides the bottleneck are an illusion." For some reason, this resonated with me much more than the chain idiom. There’s just something about building something that’s ineffective that’s more relatable to me than breaking something that’s weakly built.

He goes on to talk about the subject of "factories" and "browsers", relating work done (or not done) on browsers to a factory where throughput of work isn't optimized. He then applies this back to PHP, mentioning some of the tools that can help optimize your workflow to prevent the same kind of factory backlog. This list includes services like Blackfire, XDebug and MySQL optimization techniques.