What is Packing?
Packing is the process of converting multiple placeable actors of a single type to a singular placeable actor.
The reasoning for this is to eleviate some of the performace issues both client and server caused by excessive cosmetic actors.
Here we have 9 grass placeables. Each of these placeables replicate to your client and each of them has their own (GPU) draw calls.
When we pack these 9 grass placeables they then become 1 single actor that needs to replicate.
In summary, packing actors can reduce some of the lag caused by excessive cosmetic actors which will benefit both client and server.
You can find the list of supporeted placables here:
http://wiki.exilesextreme.com/SupportedPacking