Yes, you have to use them all, all the time. This is part of the reason for the absurd number of load combinations that are generated. The last time I did a combination generation in RAM, it was over 300. 300!!!
If you are doing direct analysis on a building that requires the notional loads to be used in combination with the lateral loads (i.e. has a stability amplifier > 1.5) you can end up with a lot more - playing around with Ram's combo generator results in...get this...1252 combos!!!!