Cant count how many times I have used this trick to get a macbook / pro to boot. Similar to the repair option in mac os/x but better.
If a mac only boots to the flashing disk or some other error then removing the drive and running this software against it may work a treat.
Keep in mind that if the drive is faulty its faulty but if not and its not the HDD cable then this is worth a bash.
Sometimes what i do after doing a full data recovery on a mac drive , if it images/clones 99.999% then I will clone it back onto a new drive and run this against it to repair the osx. Pop it back in the customers machine, boots up with operating system and data intact as if nothing ever happened. Its a bit of a party trick but when it does work like that your the hero.
* This will not work on a faulty drive and could make the situation worse, but could work on a good drive where the mac operating system is a bit wonky and wont boot.