Many blocks have inputs or outputs that do not have to be used.

Some blocks generate several different outputs, and a model may only require some of the outputs available.

Some blocks have inputs, especially inputs of the pulse type, which do not have to be used. Leaving these not connected to anything is fine, and the operation associated with those inputs (such as Reset, see Common block inputs and parameters) will never be triggered.

Blocks can, when needed, detect which inputs are connected. For example, the AND block has five inputs, but it only requires the inputs that are connected to be true to generate a true output.