In the earlier days of bridge, a direct cue bid of the opponent's opening bid was traditionally played as a 'strong cue bid', a hand too strong for an ordinary take-out double, and forcing to game. A typical hand was any 4-4-4-1 hand with 18 - 19+ HCP.

These occurred so seldom and players found they could be handled by starting with a take-out double anyhow that the direct cue bid was finally put to better use. The most popular use is to show some form of a two-suited hand.

The Michaels cue bid is one of the most popular conventions among players in the United States. You pick up your hand in second seat and you have a nice hand. You have eleven HCP but nice distribution, 1=5=2=6. And of course, you are going to open your long suit first. But hey, wait a minute. Your RHO is pulling something out of his bidding box. That's not fair. This isn't going to be so easy.

But we have lots of tools to describe 2-suited hands. The two most popular are the Michaels Cue Bid, and the Unusual Notrump. The parameters for both conventions are the same. One should have at least 5-5 distribution to start. Some partnerships restrict their use of both for hands that are either 'weak' or 'strong' but not in the 'middle' range. This idea however has been losing favor with most expert partnerships who rightly feel shape trumps strength.
The more modern feeling is that the distributional nature of their hand outweighs any disadvantage. They prefer entering the auction as soon as possible regardless of strength. That can be worried about later. We will discuss this more in later chapters