Let's say Larry the groveler is very new to SQL databases, and has just designed his first web application. Unfortunately, one of the main pages at his site has a sql query that is performing terribly, and Larry is stumped as to how to fix it. Site users are beginning to complain and Larry is starting to panic. Instead of posting an article called HELP ME PLEEZ!!!!!! on his sql provider's mailing list, Larry can put out a grovel to that same list or other relevant forums, detailing his problem and offering a lot of his own time in return for a fix to his problem.
Now, if Larry offers 10 hours of grunt time in return for a solution, Susan the SQL expert might be more tempted to help him, especially since she can probably fix the problem in less than an hour. Larry and Susan can then agree on which of Susan's projects Larry will help, and both parties come out winners. Susan has spent 1 hour of her time in return for Larry's 10 hours spent, say, documenting her latest Python module, and Larry has solved his most pressing site problem with a mere 10 hours of work.