You might not do it today or tomorrow, but you'll do it someday. You'll need to paste some content from a Web page, or a Word document, or something else that's got some goofiness embedded in it, into your Writer document.
Don't do it.
That is, don't just do a plain paste. Copy > Paste from here
gives you this.
Lots of cleanup.
Plus, when you paste from outside sources you sometimes get lots of sections. Sections are indicated, when you have nonprinting characters and text boundaries showing under the View menu, like this.
Choose Format > Sections and you'll see allllllll the little sections and how complex they are.
Why do you care? It's just icky and unnecessary, the sections will behave differently, you'll pull out your hair. Here's one example. I'm changing the left margin for the whole document, but only the section my cursor was in behaves.
So not to get into too much detail, but a plain paste will not give you what you want.
Choose Copy, then choose Edit > Paste Special (or Ctrl Shift V) and choose Unformatted Text.
And then you get this as your pasted result. MUCH better.