That way if I run into a song that has too much bass, I don't have to touch my EQ which was set for the room, I only have to modify the output going to the subs. Take a good look and listen to the quality of these items as part of the overall mixer and ask yourself if you may not be served better by an outboard piece of gear that accomplishes the same goal, which leads us to our next item. This is an option on many mixers and allows you to send an individual channel out to a signal processing unit, vocal effects processor or to a sampler. The outboard processor or sampler will take the signal from the channel, modify it and then send it back to the mixer. If you are going to add effects, processors, or samplers, make sure that the mixer has the effects loop on each channel.
Some mixers only have the effects loop on the master out section of the mixer.
The send and return feature is not commonly used by mobiles but it is an important feature to understand and originally came from Live sound mixers. A rating of 85 or better is usually ideal. This is one of the best indicators of the overall performance of a DJ mixer. The problem with this rating however is that you do not know if the manufacturer is actually telling you the truth. To further complicate the matter, there are different methods used to take this measurement.