The evolution of typefaces and punctuation was all in the interests of being easier to read. This is founded on the belief that if you want people to listen to what you say, you make it as easy as possible for them. People don't like to work hard just to read a sentence.

Type faces with serifs (like Times Roman) are easier to read than Arial. The old 'black-letter' typefaces were much more difficult to read, which is why they were replaced by the modern styles. (Look at 16th Century prints for evidence!)

Words composed entirely of capital letters are also more difficult to read, but capitalising the start of certain words gives visual cues, such as the start of a sentence. Different languages have different conventions, (e.g. German).