Programming

1. Changing the coding style substantially

Well refactoring is the only place you can change the coding style... But really a change to the coding style should not be done blindly, but with by in from team before you start changing it. It is not uncommon for a team to make bad decisions throughout the course of a project, including the style they picked. And if you ask around you might find others have the same idea as you and don't like the current style. Then you can have a conversation about it. But you should not jump in and start changing the style of a code base before you talk to your team.

One of the biggest problems I've seen is refactoring code while learning it, in order to learn it. This is a terrible idea. I've seen comments that you should work with a given piece of code for 6-9 months. Otherwise, you are likely to create bugs, hurt performance, etc.

I disagree with this. No refactoring for 6 to 9 months? That is just insane. IMO refactoring is a great place to learn how the code works. But it does need review of someone more experience to see if you are missing anything important. They can then point out why those bits are important and you just learned a bit more about the code base.

If no one else knows then what is 6 to 9 months going to achieve? The lesson here is to not refactor blindly, but to seek out others that understand the code before you refactor, and failing that spend more time trying to understand it before refactoring.

6. Overly consolidating code

Another way to put this is don't overly DRY your code. And here I would stick with the original code, not either refactor. It saves no lines and just makes the lines far longer. So much so it gives my a horizontal scrollbar on it...

But overall there are some good ideas in the post. Though I do dislike how they are using the term refactoring. All of these apply to any code you write, not just refactoring existing code.