What is the difference between CPM2C Programmable Controllers CPU Units with sinking outputs and sourcing outputs?

With sinking outputs, current flows in the following order: 
"Positive power supply line" to "Load" to "CPM2C" to "Negative power supply line". This is the same as for an NPN transistor.

With sourcing outputs, current flows in the following order: 
"Positive power supply line" to "CPM2C" to "Load" to "Negative power supply line". This is the same as a PNP transistor.

The device being output to will determine whether a sinking or sourcing output should be used.