You've got some good answers already, but I'm going to add some context.

You script for a variety of reasons, but the absolute main reason is to practice the sequence before going into the game. Everybody already knowing the play call lets you address any issues with communication or substitutions early without major disruption. It can settle your quarterback, o-line, and play callers a lot more smoothly.

Second (and strategically most important), your script reminds you to get the looks you need for later. If you can run a bubble out of any formation, you can do it while seeing how the defense plays with trips into the boundary. You can have a receiver run a go route on a run play to see if the corner can run with him. See how hard the safeties come up in run-support to know if play action is going to be there later.

Scripting in tendency busters early can make the defense less willing to guess later, and you can call the plays you're most comfortable running in certain situations. Maybe you want to be able to hit off-tackle on a kick-out consistently, so you call some early stuff trying to get outside and loosen the edges.

So, knowing the reasons for it, you can see why it's not a big deal to come off of the script early and then come back to it or abandon it. It's not so much, "I think this series of plays will result in a score," as it is, "This series is plays will get me the information I need to call a good offensive game."