If you have a malfunctioning gas system, blanks will surely make it worse. In a DI system, they eff up the BCG with carbon something fierce, even worse than Russian steel ammo. Pretty rough on the troops when you gotta have em white glove clean when you turn the weapon in. Not so much so in a piston system. One of the plusses of the pistons. I got a bunch at home- I just use them to test fire a piston build when I am done with it. 3 rounds just to test the cyclic action. My version of fireworks.
But Jon is right. Most AR's will get seriously clogged with carbon using blanks, about 200 rounds worth for one mag of blanks. If you have never used them, don't. If you actually have some training to do with them, you will need MILES gear, a laser system that costs many thousands of dollars. Don't mean to burst your bubble, just giving you facts to make an informed decision.