Normally, the input/output data to a MATLAB Function block, Stateflow chart, etc. has all these properties you can define. For example, data type, sample time, dimensions, etc.
One way to define these properties is by modifying the Simulink model file itself... but what if you want to reuse the block for different properties, or keep the definition of these properties separate from the model file?
Instead, you have the option of creating an variable in MATLAB of type Simulink.Signal. When you do this, this variable exists separately from the model so you can change your data properties without modifying the model file.
For more information, check out the following pages:
Introduction to Simulink.Signal objects: https://www.mathworks.com/help/simulink/ug/sim-signal-property-dialog-box.html
How to enable this option (it's a Stateflow example, but works the same with MATLAB Function block): https://www.mathworks.com/help/stateflow/ug/resolving-data-properties-from-simulink-signal-objects.html
Hope this helps.
- Sebastian
