For the most part they do rob HP and are only really needed at a specific level of performance/rpm. Most of us that run them on the street and on street/strip cars know that we are basically running them for the cool factor and defending their use is just an attempt to justify it.
When I told my engine builder I was going to run these, he started off with, "Are you sure because ..." I interrupted him and told that I knew I was taking a HP hit but I was ok with it because 1) my vehicles are street/strip (or what I like to call heavy street) cars & I didn't need to get every bit out of them, 2) because I have been running gear drives since the mid-80's & 3) because I dig the sound. Granted, all of mine are SBs and the whine is contained quite a bit behind the cast timing chain covers but there is definitely a whine. BBs (depending on the cover) are going to be quite a bit louder.