Publishing your code forces you to "clean it up", which can help identify errors.
As you can guess from the post title, in the process of cleaning up the code and files for uploading to the OSF, I found a coding bug. (There can't be many more horrible feelings as a scientist than finding a bug in the code for a paper that's already been accepted!) The bug was that when calculating the accuracy across the cross-validation folds, one of the fold's accuracies was omitted. Thankfully, this was a 15-fold cross-validation, so fixing the code so that the mean is calculated over all 15 folds instead of just 14 made only a minuscule difference in the final results, nothing that changed any interpretations.