The closer the numbers are together the more time is wasted trying to be exact about them. Fib helps reduce the amount of back and forth. If you need to guess how much something weighs and your options are 1,2,3,4,5,6,7,8,9,10,11,12,13,14.....100, you are going to have a lot harder time achieving consensus than if you asks "Is it heavier or lighter than a breadbox?"

At least that is the idea.