That is a good question! I think that people get caught up on keeping a sterile environment free of weird pests and creatures that hitchhike on live rock. But if possible, for example, You were looking into 30 more pounds of rock, I would do 50/50 BRS reef saver and live rock. If I were shopping for live rock, I would look for the most creature rich rock you can find. Some local fish store sell rock packed with coralline, sponges, worms, fan worms, micro brittlestars etc etc. Now some of that rock can come with aiptasia, vermitide snails, asterina stars and/or unwanted crabs. To me though, it's a learning experience and it really helps with the bio diversity. Most of the pros go for live rock and skip the dry rock but it's more cost effective to mix your rock as it will seed the dry rock.