It is important to note that deca contributes to intramuscular fat gain, which is very very hard to distinguish from lean muscle. You can measure bodyfat, intracellular fluid retention within the muscles, the extracellular fluid retention and fat levels outside the muscle, but to actually measure intramuscular fat levels is very very hard. Mainly because fat can at time have the same density of the muscles (especially in non weight training patients.)
Deca was RX'd in the past because of the benefits of (potential) intramuscular fat gains (in addition to the muscle preservation properties the anabolic side contributing to combat wasting) for HIV patients because of the popularity at the time of the addition of AZT, Retrovir, Epivir, and Videx to the common protease inhibitor cocktails out. These compounds are known for contributing to the rapid fat loss that HIV patients experienced.
As the cocktails were improvished with new meds and as the old cocktails utilizing the nRTI compounds were deemed not suitable for the first phase of treatments for patients, the use of deca in HIV has started to decline over the last few years.