exhaust differences

[xr8-ute]

hi, i'm just doing my research on exhausts before i get mine done, is there any difference between a full twin exhaust system, and a system that collects before the muffler? The vehicle is an au11 xr8 ute. I have noticed that most shops will fit out a single system that collects before the muffler while other people run a twin system all the way through. Thoughts and advice much appreciated.