Default Can some witty dev help

Just wondering what it means growth limit if the heap size is 128m is it saying that 64m is the max even though 128m is available or something else? I was scrolling through my build.prop just checking things out to see what is tweaked and found this never seen a growth limit in a build.prop

This is a high density device with more memory, so larger vm heaps for it.
# For ICS project, default 32m/48m
dalvik.vm.heapsize=128m
dalvik.vm.heapgrowthlimit=64m
dalvik.vm.heapstartsize=8m

Sent from my ADR6425LVW using XDA
Sent from my rezound
Rom: Sense 4.0