Space matters. Space helps us discern one word from the next, one thought from the next, one paragraph and page from another—it is, in short, the best way we have of making sense of the world. The moon is far from the Earth. The Earth is further from the sun. The sun is further from other suns. And galaxies further from other galaxies. It couldn't be any other way. And so it is with words, sentences, and paragraphs. Look at paragraphs: they used to be delineated by simple indentations.
But today—we recognize the value in spacing them apart with a blank line. We know this. We do it instinctively now. We do it because paragraphs are more important than sentences—and those blank lines are more helpful than indents in helping us navigate our text. Paragraphs deserve that line. We deserve that line—a space to stop and think and consider before moving on. Sentences, likewise, are more important than words. They deserve that extra little space to breath—a pause, a break. An intermission, if only a small one.
I don't put two spaces after a period because of typewriters or proportionally spaced fonts or because I know that AP Style is for journalists with space constraints. I put two spaces after a period because sentences matter. Space matters. The written word matters. It's music—and without the space between the notes, all we have is noise.