Basically the contention is that even if you have a logically separate piece of work, sometimes it's better to go ahead and write it inline in the larger function, because it makes the code flow more linear and imperative and thus easier to read and debug. There are also obvious disadvantages to writing code inline - less strong separation of functional bits, temptation to copy-paste code, less ability to debug and test functions independently, etc. etc. All the pros and cons are obvious and thus not interesting.
The key point to me is the issue that while code inline may be a win sometimes - it's a big loss at other times, and it requires you to make a careful smart logical decision about which way to go.
That's very bad. I think most smart people as they get older come to the realization that you shouldn't put yourself in positions where you have to make careful logical decisions over and over. Instead you should craft habits and rules for yourself that help you do the right thing without having to make careful decisions.
One obvious case that most smart people figure out is diet and exercise, or booze or other indulgences. Yes, it's perfectly fine to have a some dessert once in a while, but if you open that door for yourself you're putting yourself in a situation where you are consciously making a decision "is it okay for me to have cake today?" and you will inevitably get lazy and make the wrong choice sometimes.
As usual the best analogy is poker, and it's how this point was really made real for me. Smart people often start out playing poker trying to logically reason out every single action and think they don't need to be constrained by simple rules or habits. That's great if you really are correctly thinking through every situation, but you inevitably get tired or lazy or make mistakes, and if you're not constraining yourself with rules, you can make huge mistakes.
For example, there might be cases where the best play is to limp aces up front, or to not reraise with aces, but correctly making that decision requires a lot of careful thought, and the upside to making that decision is pretty small, while the downside to doing it in the wrong situation is very big. It's best to just make a rule for yourself that you always raise or reraise. It simplifies things, it removes decision points and lets you focus on more important issues. It might be +EV to call raises sometimes with hands like 68o, but it's best to just give yourself a rule that you never do that.
To be clear - these rules are specifically non-optimal. By making rules for yourself you are intentionally choosing to not try to be 100% optimal, so of course someone can say "you could have done something better there". That's not the point. The point is that if you try to make perfect decisions all the time you will occasionally fail very badly.
Winning poker play (or good coding, or good life living) are largely about making it easy for yourself to do the right thing.