No question continuity is important. But if all you do in practice is run your motion against your defense, your defense gets locked into that motion. And yes, there are options, but the defense knows the options, and the kids naturally get lazy.
Now, I'm an anomaly -- I'm a defense-first coach. I'm not very good at drawing up plays in the huddle, and I focus more on fundamentals than complex offensive motions. And I've found that the best way to improve my defense is to let the offense freelance during open gyms and sometimes during practice. That way, defenders cannot anticipate what will happen next nor adjust to options.
Let me put it another way: Over the years, we see offensive systems come and go. Flex, the Triangle, Dribble-Drive Motion. What happens is that when they are first introduced, defenders are surprised by the cuts and options. But over time, defenders learn, even if not directly instructed in how to adjust, and the offensive system is replaced by another.
Which basically means no matter the options in a motion, defenders will adjust. And if your defenders in practice face the same motion over and over again, they will adjust -- they will cut corners, they will get lazy. Which then means the defense your motion faces in a game is considerably different than the defense your motion faces in practice.
Working on offense is much more fun than working on defense, because players like to score and handle the ball. But sooner or later, you have to be able to defend against systems and plays you never see in practice, or in previous games, and you have to be able to respond to the unknown.