For us the physical labor was about two things - removing them from the immediate environment that was provoking the inappropriate response and about providing an outlet for the anger that was both appropriate and, as BWBShari mentioned, allowed them time to think out the problem.
For me there is a difference between feeling good about helping out and being responsible even when it doesn't feel good. Both are important. There are times in the workplace where you have to suck it up and do things that you resent, that you don't want to do, but that if you don't, the consequences will be severe. Teaching kids - especially teens - to have the self control to choose to do things they don't want to but that they need to do is just as important as making sure there are other experiences that allow for feeling good for contributing to the good of the family.
And one of the best reasons to use physical labor to deal with anger in a child is that physical labor almost always produces an immediate finished product that creates a sense of pride. A completely weeded garden, a shoveled driveway, etc. all create something immediately that they can be proud that they did. It replaces the inappropriate behavior with a positive outcome not only for the change in attitude but the sense of pride (whether they'll admit it or not) in what they improved physically.
