Here's why:
* Modern typography: The two-space rule originated from the use of typewriters, where the spaces were physically wider. This is no longer necessary with modern computers and fonts.
* Readability: One space creates a clear visual separation between sentences, making text easier to read.
* Consistency: Most style guides and publishers follow the one-space rule for consistency.
So, unless you are specifically instructed to use two spaces, stick with one.