This effect marks the asset as complex - meaning that it is intended to be a single 3D model that contains a number of individual assets.

When given this property, the 'host' asset (the actual asset the 3D model is assigned to) is not selectable. But all child objects are.

You can perform something similar with Unselectable, using a local parameter of 'yes'.

None.

<complex/>

This asset can not be clicked on or highlighted, but its children may.