The guy who told you to scrape coral is an idiot. Whether scuba or apnea, no diver should be destroying the reef. Fortunately I don't see this too often among spearfishermen. Nevertheless, those that do beat the shít out of their spots until everything is dead, then wonder why there's no fish or regulators want to ban spearfishing are their own worst enemy. A responsible hunter practices conservation. Whether aquatic or terrestrial. You kill the coral, the small life dies. The small life is what the fish eat. No more food for fish, no more fish for you. The most common and correct way to attract fish to you is to use flashers or toss sand up in the water column. I do neither and flashers are more common for blue water pelagic hunting.
Breath hold spearfishermen will often hug the reef, but they shouldn't destroy it. Frankly, I think it makes little difference for most species. Scuba spearfishermen aren't sneaking up on fish, you're loud blowing bubbles, yet they can still keep up with apnea spearfishermen for the most part. Still, the best technique is to not be at the same depth as the fish. For reef fish you want to be around 5m/15ft. above the fish. Fish use their lateral line to help judge size, distance and threat level. This is why they turn broad side to divers. If you're shooting fish at the same level they are going to detect you much faster, also the shaft will often go straight through the fish. This is undesirable whether lineshafting or freeshafting. Freeshafting you will lose the fish if you did not stone it and with lineshafting it will end up on your line. Now you're wasting time trying to secure the fish off your line and making a bunch of commotion scaring away other fish and attracting sharks. Not to mention your shaft and line is laying flat on the reef raking all the coral. Lateral shots will work on bigger fish as there's more meat and bone to stop the shaft, but for smaller fish you're just going to create problems for yourself.
If you're shooting down on the fish it will still give you it's broad side, but you can put the correct angle shot on the fish and the shaft will stop on the hard bottom or sand and do far less damage to the reef. It also prevents the fish from ending up on your line and with that correct angle, about 45°, it will pin the fish or force it to swim down where it cannot get off the shaft due to the flopper, allowing you to quickly secure it without ever having to touch the reef.
Here's a pretty good example from a video last year of a mix of both good and bad. Shots that were taken lateral turned in to more work. I nearly lost one fish off the end of the shaft and you'll note when my buddy shot at the one fish near the end, the shaft went straight through it. Fortunately I was there to finish the job. While these videos make it appear we're on the bottom, we're not. We're either in trim or slightly inverted.
You should be leaving your spots the way you found them.
Watch how a pro does it. When you're good you can get away with lateral freeshaft shots.
