benefits are a sustained unchanged level of test in your system, without having to trust your endocrine system, at a level high enough to maintain gains, but not high enough to have crazy sides. gains are much slower, but you arnt going to crash and lose anything, and your health (lipids, blood pressure, estrogen sides) will be "fine".
negatives: you will probably never be able to come off after a while, and what happens if you cant get test, always having to inject, etc etc