"I hear pros hardly ever use it"---This is just not the truth. I know many who are professional who will use multibands from time to time. They do exactly what you say--they clean up the mud and make everything tighter and punchier (IF YOU KNOW HOW TO USE THEM). That being said, if you really don't know WHY you're using it, then you probably shouldn't be. I use them in mastering to catch peaks after EQ, especially if I just boosted the mix. Use your ears as the judge. The settings are CRUCIAL to making them work correctly, and that comes down to hours of working with it.
For starters, for light compression as in acoustic work or indie rock etc...stick to low ratios and high attack/release settings.
For metal like you're using, the attack and release are usually lower settings to get more "punch". Even for metal though, never use higher ratios than 4:1 for multiband, you'll kill your song. If you keep all bands the same ratio, that helps keep it more natural sounding and also if you don't compress the low and upper mids as much as the low and high, that will help too. But like I said, it's all an ear and experience thing.