The “Add Pin” bit automatically shows up on certain nodes, for instance a Multiply node (float * float), Subtract, Add, or a Sequence node (among others) has the Add Pin by default. If you add pins that you don’t need, right click on the pin and you can choose “Remove Execution Pin” to get rid of it.
So basically it is added by default to nodes where multiple inputs make sense, there is no way to add it to a node without it. 