With a conventional automatic if the car has a good (and convenient) parking brake you can choose to leave it in D and hold it on the parking brake. Or, more wisely, if you are stopped for more than a matter of seconds, put it into N and hold it on the parking brake. Do not simply stand on the footbrake whether in D or in N and blind the driver behind. (Especially if you are driving a Mercedes CLC that has a huge third brake light.) A DSG doesn't have a torque converter that can withstand churning against itself while the car is braked in D. Instead it has two 'wet' oil clutches, one for each shaft of the transmission. So wear on these clutches is more likely to be promoted while braked in D than with a torque converter automatic.