Artists can solo shading nodes and sections of material networks using the Visualizer node, to aid in lookdev and artist control.  

To solo a node or incoming shading network, simply select the node you wish to solo and press the X key.  Doing so, will insert a visualize node and automatically connect the output of the selected node into the input of the visualize node. 

To 'un-solo' a node, cut the input to the visualize node and continue working on the lookdev.