Help undestanding ofxCv Flow

hi,
i’m trying to understand how optical flow works in ofxCv. this might be a very simple question but i cant understand why in almost all the examples i found i see this:

ofxCv::FlowFarneback flow; 
ofxCv::Flow* curFlow;

and then calculate the flow like this:

curFlow = &flow;
curFlow->calcOpticalFlow(camera);

why using the Flow* if you can access the calcOpticalFlow method from the FlowFarneback?

thank you.