There are two copies of the RNA in the HIV virion. These are retroviruses. So, they can make cDNA from even just one copy using reverse transcriptase.
What is the use of the other? Are both integrated into host chromosomes?
My guesses are:
To ensure increased chance of getting integrated. But, if one gets in, the other also should be able to.
To increase the amount of protein translated (if both get integrated).
Two for two sets of chromosomes. (Seems juvenile but still a possibility. although, I do not think there are specific sites of preference for the viral DNA. Are there?)