Handwritten code Development vs. Model-based design

Greetings,

I am kind of new to matlab and I am learning MBD using SIMULINK.. I went over the benefits of MBD and how it makes everything easier, still I would like to understand its limits and when do we prefer handwritten code over it ( some real-life examples that embody choosing Handwritten code over MBD would be very appreciated too).

Thanks in advance!