Mostly that simplicity and clarity are hard to achieve but very worth it. Learning what it feels like to correct and simplify logic into something that is easy to read and easy to verify is experience that has transferred well.
From my experience:
Everything you publish in science/academia will be read by a wide, potentially hostile audience. It is very easy to be misinterpreted, and misinterpretation wastes a lot of time and effort.
Stating what you mean in clear, precise terms is far more work than writing things that make you sound 'smart'. Good writers make their work seem terribly obvious, but it comes at the labor of many, many drafts. Most of the hardest work in editing is helping an author subtract and simplify to get right to the point. The labor of being precise and explicit exposes errors that the illusion of understanding tends to conceal.
Young/inexperienced writers often have a gigantic blind spot when it comes to their own writing, and correcting that is a very painful process.
Also, sometimes the original author was right, and the only precise way to express something was really ugly and horrific and your attempts to make it simple did violence to a lot of careful thought.
The world would be a better place if everybody took the effort to make their point with precision, simplicity and clarity.
However the truth in many situations is that if person A spends an hour constructing a beautifully worded five-liner, and if person B spends the same time to produce several rambling pages, then person B's argument may well win out. Readers who have spent ten times as long wading through B's contribution are quite likely to have forgotten entirely about A's.
