For example, the sound of the letters "B" and "P" sound pretty much the same if you don't have a very clear connection. You wouldn't want to say, "The general has a big heart" but be heard to say, "The general has a pig heart." Spelling it out by saying "B-I-G" doesn't help at all. But saying "Bravo-India-Golf" clears it up.
That was a pretty lame example, wasn't it?