You can now quickly change the transparency of the all components in an assembly or all bodies in a multibody part. SOLIDWORKS 2018 has added a Transparency option that applies all components. Right-click on the top level feature in the FeatureManager Design Tree and choose Top Level Transparency.
For components that were already set as transparent, they will remain transparent if this option is selected and deselected. If the same component is set to opaque when the Top Level Transparency is applied, it will remain opaque when the assembly returns to opaque.
The transparency setting is shown in the Display Pane for each component, including each component within subassemblies (but only in this top level assembly). This applies to both Shaded with Edges and Shaded modes.
This can be toggled off by returning to the in-context toolbar and deselecting Top Level Transparency.
You can modify individual component visibility while in the Transparency mode to have them highlighted. This can help where you want most components transparent with a couple opaque. In this case the overall Display Style is set to Shaded to avoid too many edges, and the bearings set to opaque and shaded with edges.
These display settings can be saved in a new Display State for future use.