How to show spaces and paragraph marks on screen
Press Ctrl+Shift+8 in Write by Zaweba to show dots for spaces, arrows for tabs, paragraph marks and labelled breaks. They never print or appear in PDFs.

Press Ctrl+Shift+8 in Write by Zaweba. Formatting marks appear on the page: a dot for each space, an arrow for each tab, a paragraph mark at the end of each paragraph, and a labelled marker for each break. Press it again to hide them. They show on screen only, never on paper or in a PDF.
Why you would want to see them
Most of the time, the invisible characters in a document can stay invisible. But when something on the page looks wrong and you cannot see why, they are usually the reason. A line that will not align with the others has a stray space at the start. A list that will not line up was spaced with a mix of spaces and tabs. A heading that jumps to the next page has a page break in front of it. A gap between paragraphs that will not close is an empty paragraph.
Showing the marks turns guesswork into a quick look.
Reading the marks
Each space shows as a small raised dot, so two dots between words means a double space. A tab shows as an arrow, which tells you the text is using a tab stop rather than spaces. The paragraph mark appears wherever you pressed Enter, so you can see empty paragraphs and the end of each real one. Breaks are labelled, so a page break, a column break or a section break is named on the page and easy to tell apart.
Fixing common problems with marks showing
Double spaces after full stops are easy to spot as pairs of dots. Find and Replace can clear them all at once, and with regular expressions ticked, one pattern catches every run of two or more spaces.
Lines indented with spaces never quite line up. Delete the spaces and use the paragraph's indent setting, or a tab, so every line starts at the same place.
Empty paragraphs used as spacing are fragile, because they move about as text changes. Delete them and set spacing before and after in the Paragraph dialog instead, so the gaps stay even.
A stray page break leaves a short page with nothing at the bottom. With marks showing, the labelled break is easy to find and delete. Section breaks are worth care, because each section can have its own page setup and columns, so check what it controls before you remove one.
Text from elsewhere
Text pasted from emails and web pages often carries extra spaces, tabs and line endings. Showing the marks makes it clear what came in. Paste as plain text in the Edit menu avoids bringing in odd formatting, though the spaces and line breaks still come with the text, so a look with marks showing is still worthwhile.
Documents opened from other word processors are worth a look too. A .docx, .odt or .rtf made by someone else may use spacing habits you would not, and marks show you what you are working with before you start editing.
Nothing reaches the page
The marks are a view, not part of the document. Write shows them on screen only, so they never print and never appear in an exported PDF. Leave them on while you tidy, then turn them off to judge how the page really looks.
It is a small switch, but Ctrl+Shift+8 in Write by Zaweba explains a lot of mysterious layout problems in seconds.