I don't know, this is good advice perhaps for things which are not important.

But, if you are writing an email to a person whose time is valuable, better not to do it quickly. Save a draft, come back to it tomorrow, read again, then send.

If you are writing a legal document, don't do it quickly. Write it, come back to it again to review. Is it still a good idea?

If you are doing something completely new, do it slowly and step by step -- if it is new you don't know if it is right without checking each step.

If you have an idea, read the literature, patents, see what is out there first.