RLVa is safe. Simply enabling RLV will not invade your privacy, lag your viewer or cause you to breach the Second Life terms of service.
RLVa only functions on worn attachments. Other rezzed objects require an RLV Relay to work as a proxy and pass their special commands on to you. If you don't wear a relay device, you are simply immune from all external attempts to utilise RLVa on your viewer.