In my family they always par boiled the brats. But I honestly think this was done out of fear. The same way my mom turned pork chops and turkey into jerky. Indirect cooking had not been invented yet.
Pappy I couldn't agree more with you! All of our pork got boiled before whatever finishing method. The fear was trichinosis (sic). So sausages including bratwurst got boiled before grilling. So much of this was tradition. Some traditions are good, some are not, it's all a personal choice as to what trips your trigger! I used to boil brats...because everybody else did. Until I happened into the meat market that makes the best bratwurst I have ever had.( Miesfeld's in Sheboygan, WI) One of the butchers told me not to pre- boil but to grill without breaking the skin. Before grilling tho, a twenty minute swim in cold water firms up the casing.
If they won't be eaten right away, a holding solution of beer, butter, and onions is used.
It's all personal choice to choose your favorite methods, but the most important factor is to ENJOY!