Virtualize is useful if you have a larger number of continuously looping point sound sources around a scene, such as torches in a castle. If you have 80 torches in the scene, and the instance limit is 5 with Virtualize, only the nearest 5 torches will be audible. As you move through the castle, whenever you enter the audible range of new torches, they will become audible and the ones further back will get virtualized.
If you use Steal Oldest in this kind of a scene, it is not determined in which order the torch sounds are started (depends on how the scene is loaded, and in what order the instanced objects are in the scene database) so only a few undetermined torches will be audible. If you use Steal Quietest / Furthest, only 5 torches closest to the starting position will be audible, the rest are stolen (aka stopped) and will not become audible when approached.
In short:
- Stealing is useful for one-off / transient sounds that keep getting triggered (like footsteps)
- Virtualize is useful for continuous / looping sounds placed into the scene (like rivers or torches)