karma has a lot of interesting subtleties. It's been expanded upon for a long time, but that doesn't mean we can't find modern metaphors for older concepts.
Credit for the translation of the concepts and the application of the metaphor go to my sanskrit teacher, "Dnyanada" (no last name, and in fact, she had a great story about how she got rid of it years ago, and when she came to the US, no one could comprehend the fact that she chose to not have one. The computers had a field-day with that one!).
My sophomore year at Rutgers was when I took sanskrit, and Dnyanada often went on tangents about certain tidbits of information. She took a stance against "sanskritizing" and recreating etymologies for words in modern Indian languages, for example. While these tangents didn't directly correlate with our lessons, they did provide a useful boost of interest for others in the class, but I loved the trivia.
One day in particular, she talked of karma being misused and happened to mention two interesting types of karma. Now, I don't know her sources, but she was a well-read woman and so I will take her word as a secondary source to this, especially considering just how much she knew of everything we brought up. She described how further developments on the theories of karma led to what we might in this day and age call "credit" karma and "debit" karma.
"Credit" karma is what we face when we act on something, spontaneously or not, and for which we will later reap the fruits of. Whether we're eating dairy and we're lactose-intolerant, or we're gossiping about the coworker two cubicles down, it's all credit karma here. This doesn't mean that we are acting completely originally; when it comes down to it, nearly everything is a reaction. The distinction here, however, is that the real, dominant fruits are forthcoming.
"Debit" karma, on the other hand, describes the karma "used" when we react to something. Here, we're acting from fruits we have come to acquire without having actually acted. Revenge is an excellent example. Let's say actor A does something horrible to actor B. Actor A created credit karma. Some of the fruits of this action have gone to Actor B and motivated him to seek revenge. When he finally acts, it will have been out of debit karma. This situation primarily applies when actor B did not instigate actor A, or if actor B somehow acts out on a third actor, actor C. Otherwise, it really is no different from standard reaction.
To extend the metaphor, we can act from our checking accounts or our savings accounts. If we act from our checking accounts, we are acting on karma that is marked "to spend." This is often recent karma. When we react on things that are more or less direct, then this is from checking. This applies in the above case when actor B happens to be irate from actor A's actions, but takes it out on actor C. We can say that his acting out on actor C was because he was still under the influence of A's actions. He was still angry and so it passed on this way.
For a moment, let's take a look at a completely different example. A husband gets home late from work irritated about his boss. His wife cooks him a meal, but he doesn't like it. They argue. That's from his checking karma. But, let's say his wife takes a cheap shot at him during an argument when she's right. He doesn't argue and goes along with it because, after all, she is right. A week later she argues with him about something else and she's wrong. In his anger, he suddenly remembers the lousy feeling from her comment previously. He's further infuriated by this and now he says something that crosses the line. This action is savings karma. For a week, he was not bothered by her comment, thinking that he had let it go. Then, in a separate event, that comment comes up and helps to propagate whatever he's thinking at that time. Because of the comment's dormant period, we can say that it was put into savings. Later, he remembered it and used it to fuel something else, i.e. he transferred it into his checking account before using his debit card.
Why on earth is this useful to us? Aside from being yet another tool that lets us further analyze and understand our actions, it directly calls into question our motives. Direct karma (credit karma), redirected karma (debit, checking), and forced-direct karma (debit, savings) help to explain why we do things. The danger here is not unfamiliar, however. People have a way of using whatever they can to justify their actions.
karma, however, is a law of the universe. We do not have a choice to participate or withhold in its games. No matter what actions we take, we are most definitely influencing something and that yields reactions. The benefit to us would be to see patterns and tweak our behavior to benefit us. It's fine that things go into our savings accounts. We shouldn't spend on stuff that's frivolous, though. If we're saving for something, like fuel during our workouts, or inspiration for songs, or something else that acts as a positive channel, then we're hacking the system to our benefit. And, we need to know when act and how to make it productive. And, when to let go.
I'll bet this really brings more meaning to the old adage, "Don't write a check your butt can't cash."