Trick question there isn't it? lol lots COULD go wrong. Very wrong.
But with that said...I have done 5 weddings myself, all for free except for one who gave me a gift and they all were very pleased. But, they were all friends with the exception of one who lost their photographer a few days before the wedding and none of them expected those "awesome shots" that wedding photographers can get so it worked out fine for me. I had to have a Speedlite flash or I would have been completely screwed. *I* am not happy with the quality of the pictures but the people were so I guess that is what matters. IF the people know and are willing to accept that 95% of the photos might be completely screwed up and there's not likely to be anything extra special then why not...but I would have them ask family and friends to bring cameras too. I wouldn't accept any money for it (unless it's a gift) until you are truly experienced.
But most people here will probably say no, no no don't try it. and for the most part, they're right

I think you want to try it to see how you do, for the challenge...understandable, but I'd shadow the pros instead.