....and do I need to put it back?

I just finished installing an aftermarket cat-back exhaust system and I noticed the strap bolted to the front of the stock muffler. What is it's purpose?

 

Exhaust gas motion through the exhaust system can create a lot of static electricity. This needs to bleed off unless you don't mind the occasional zap that could get into some of your sensitive digital circuitry in the wrong place. I would keep the strap in front of any joint in the exhaust system for best bleed-off performance. If all the joints are welded, the strap position won't matter.