On the internet, you can find many guides on micro-optimizing PHP, for small applications, these optimizations do not add any value to the application performance. In medium to large applications (depending on the complexity of the processes implemented), the summatory of all that saved overhead could improve the overall application performance.
Early optimization is the root of all evils, most of the time you need to be focused in creating amazing and maintaniable software rather than faster software. The following tips help to write faster PHP code, however if the volume of overhead saved is not considerable the application will perform without a noticeable difference.
Be aware of the difference between code that is compute-bound (slow because it's doing a huge number of instructions) and code that is I/O bound (s