I don't use "quick-and-dirty" as a derogatory term, so mostly I mean no error checking for rare occurrences or not ensuring correct values are being passed through. An example would be in Python if I just write MatrixA * MatrixB without any checking. I should check that they are both matrices if that is what I want, and that is what I did for reusable code. For one-off data analysis or computation, no-checking is certainly quick.