Techie,
I believe the benefit of the "property node value" is that it does not require a copy of the data to be made in memory like a "local variable" would. From what I understand LabVIEW keeps a copy of the data for each local variable in the code. So if my code occasionally updating a front panel graph that has a lot of data, I use a property node since speed is not an issue and I don't want to eat up memory with multiple copies of data. But if I wanted to quickly update a front panel graph with small amounts of data, I would use a local variable. Where is the break even point? I don't know. You can always test it out if you want to find the optimum choice.
Mark