This is a quote from "Clean Code"--a quite renowned book by Robert C. Martin:
The Total Cost of Owning a Mess
If you have been a programmer for more than two or three years, you have probably been significantly slowed down by someone else’s messy code. If you have been a programmer for longer than two or three years, you have probably been slowed down by messy code. The degree of the slowdown can be significant. (...)
For me the first two sentences bear exactly the same meaning and I am at loss of why they were written next to each other (to the point of suspecting the author to placing a pun on bad style of coding).
What is the semantic difference between the first two sentences that both the author and the editor decided to include?
Author uses this kind of stylistic repetition throughout the book:
Have you ever waded through a mess so grave that it took weeks to do what should have taken hours? Have you seen what should have been a one-line change, made instead in hundreds of different modules? These symptoms are all too common. (...)
Let’s say you believe that messy code is a significant impediment. Let’s say that you accept that the only way to go fast is to keep your code clean. (...)
However in these cases the phrases have clearly distinct or complementary meaning. This is not the case for the passage in question.