I've got one and the only reason i got it was i cbf with headaches sometimes from my exhaust /drone as said above by Kez but also i have very good neighbours who all respect each other and id like to be quiet when i come home numerous times in the early morning with my car..
EPA's are less of a headache as u get pulled over and they check to see if ur cars loud and they notice its dead quiet. just gives you less headache.