I'd bet that a reason the first line indent was invented was as a space-saving method of indicating new paragraphs. Do we skip a whole line and waste paper, or ... ? "I know! We can put a bit of extra space before the first word of the next paragraph!"

Such things are not required in digital media where each reader might have completely different spaces for text to render within. And, ideally, the content and its formatting are structured in such a way as to allow the user to apply their own formatting if desired.

warning & disclaimer: post may contain factually incorrect guesses and suppositions of the author; no information herein should be considered accurate or factual; use at your own risk