Simplifying your code for performance can and should be done throughout development. Complicating your code for performance should only be done after profiling has been done and bottlenecks have been identified.
During the entire development process it’s good to constantly refactor. Reducing all extra steps and other cruft in a programs logic can not only improve performance but it makes your code more readable and decreases file size. Reducing it to it’s poetic essence isn’t what the Knuth was talking about when he said “Premature optimization is the root of all evil.”