You can either create "value" for or remove "value" from your community. This is defined any way you want, including financially, and it is defined differently by different folk. Nevertheless, it is pretty easy to tell when someone spends all their time AddingValue and when they're always SubtractingValue?.
The human mind is an effectively unlimited resource, as long as you don't squander it. There is an infinite amount of "value" to create, but our CulturalAssumptions force us to believe in the limited nature of resources and options we have open to us.
I believe you can both add and remove value simultaneously and that is the most appropriate model. No change is "pure" and only does one or the other. This is also why it is not true that it is easy to tell when someone is adding or subtracting value.
Yeah, well, it's usually a good idea to ask what you can do for someone, before up and doing it. That's a good way to determine what you can do to create value in their lives.
About the only thing you can do with a computer is add value to it. When you write a program, you make your computer more useful to you, and therefore more valuable. When you write a document or print something off, the net value of the computer (financially even) goes up.
What about deleting all files from the hard drive? I'd call that subtracting value. The same for writing a program that undesirably does this (in other words, a virus). On the other hand, a program that deletes all files from the hard drive could be adding value if it did so as a result of the user's intention (they really wanted to get rid of everything). It's all a matter of perspective and attitude.
Do you work for free? If you get paid at all, you are costing value. Also, if you have a poorly done software program it may cost the user more in time and effort to use it than not to use it. Just taking up space on the hard drive subtracts value. Everything has costs and benefits.
I wonder if it would be fair to say that any system with self-motivated people requires the addition of value to that system for collaboration to occur.
Person X values sheep more than gold, because he wants to shear them, while person Y values gold more than sheep. They make a trade. Person X walks away with more value than he started with, and so did person Y, meaning that value was added to the community without any real work having to be done except resource allocation.
Now, if Person X sheared the sheep and then sold the wool to Person Z, Z would probably give something that X values back as well, but they would both feel that they had profited. By doing work, you manage to circumvent a lot of the problems associated with thermodynamics. Markets are thermodynamic systems only when they are closed.