X pipe, Y pipe, NO pipe

Trying to decide on exhaust for my 340. I put it in my Dart which was originally at 273 and has a 2 to 1 pipe. I was thinking about just cutting off the 2 to 1 and extending the pipes back with mufflers. Then I started reading about X pipes and Y pipes and how those assist with exhaust. If I don’t put one of those on what’s the worst that could happen? I assume they’re not absolutely necessary as I’ve seen others run straight pipes back with mufflers.