Having done a variety of data analysis and computational modeling while working as a PhD physics student and postdoc, I can attest that many of my colleagues wrote terrible code.
The problem wasn't that their code didn't have a nice user interface, or wasn't designed for reuse. The problem was that it was often impossible to really know whether it worked correctly or not.
In my experience, whether the code you're writing is going to run once or go into production, it needs to testable and understandable - enough that you have confidence that it does what you think it's doing. And that means building it in small enough pieces to analyze. Otherwise you just don't know.
The problem wasn't that their code didn't have a nice user interface, or wasn't designed for reuse. The problem was that it was often impossible to really know whether it worked correctly or not.
In my experience, whether the code you're writing is going to run once or go into production, it needs to testable and understandable - enough that you have confidence that it does what you think it's doing. And that means building it in small enough pieces to analyze. Otherwise you just don't know.