Perhaps the most controversial space in the world of style is the one that comes at the end of a sentence.
The traditional practice in business and government was to add 2 spaces after a full stop before the next sentence started. In the age of the typewriter, this was to ensure there was enough space between sentences, as typewriter carriages could vary in movement.
In the age of the word processor, the spacing between sentences is precise and certain, so the more efficient single space is all you need to add.
