This simplifies meshes by turning off particle data. In large scenes with multiple particle modifiers on multiple meshes it can become quite taxing on the cpu. Even with 0 display since the particle data is still bound to mesh it can make working with mesh very cumbersome. This disables the particle system in the scene so the objects can be worked on without the particle system eating up cpu resources.
Enough changed from the last checkins of this work that a new commit was best choice.