Some abbreviations don’t have periods, such as “NASA.” And we pronounce it like a word. But some abbreviations are easily misunderstood without periods. For example, the abbreviation for “United States.” Without the periods, the U.S. might be treated as a pronoun. See below:
When I first saw this, I considered making it into a lesson about “we” and “us.” Then I read the whole sentence. Saying “U.S. diplomats” would have removed the ambiguity, wouldn’t it?
Periodize your abbreviations when you need to remove ambiguity!