Lube in general helps prevent the spread of HIV. As long as the lube itself is not an HIV-carrying fluid (cum, blood, vaginal fluid, breast milk, cerebrospinal fluid - and WTF is going on if you're using cerebrospinal fluid for lube, anyway?) generous amounts of lube helps prevent tears from opening where HIV could enter the body. It's not a replacement for condoms and communication, but it's indespensible none the less.