In general, progressive�is used when you want to emphasize a process over time.
Your first example is a simple statement of fact.
Your second example conveys a sense of the time involved.
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In other senses, the difference is bigger. (when not using "since" or "for")
I have painted the living room. -- The job is finished.
I have been painting the living room. -- The job is�probably not finished, and the emphasis is on the process over time, rather than the result.
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Bruce�