From the groff-manual at gnu.org

5.1.6 Input Conventions

Since gtroff does filling automatically, it is traditional in groff not to try and type things in as nicely formatted paragraphs.

: this conflicts with reST because a reST-document is nicely formatted WYSIWYH.

These are some conventions commonly used when typing gtroff text:

• Break lines after punctuation, particularly at the end of a sentence and in other logical places. Keep separate phrases on lines by themselves, as entire phrases are often added or deleted when editing.

• Try to keep lines less than 40–60 characters, to allow space for inserting more text.

• Do not try to do any formatting in a WYSIWYG manner (i.e., don’t try using spaces to get proper indentation).

5.1.3 Sentences

Although it is often debated, some typesetting rules say there should be different amounts of space after various punctuation marks. For example, the Chicago typesetting manual says that a period at the end of a sentence should have twice as much space following it as would a comma or a period as part of an abbreviation.

gtroff does this by flagging certain characters (normally ‘!’, ‘?’, and ‘.’) as end-of-sentence characters. When gtroff encounters one of these characters at the end of a line, it appends a normal space followed by a sentence space in the formatted output. (This justifies one of the conventions mentioned in Input Conventions.)

In addition, the following characters and symbols are treated transparently while handling end-of-sentence characters: ‘"’, ‘'’, ‘)’, ‘]’, ‘*’, [dg], [rq], and [cq].

See the cflags request in Using Symbols, for more details.

To prevent the insertion of extra space after an end-of-sentence character (at the end of a line), append &.