After setting your levels, exercising the stereo field becomes next in the process. With pan positioning and achieving stereo width, you create clarity, especially with mono sounds. Mono sounds will all fight for the centre spot creating masking, a lack of clarity and a lower sense of excitement as stereo width is not being utilized. Some sounds are mono and some sounds have a combination of mono and stereo signals.
It’s important to know the context of stereo and mono information in a sound. This will help better determine the placement of an instrument. If signal is partly stereo and partly mono, it already has width within itself, thus when using pan pots, the stereo image is displaced too.
Time-based audio effects guarantee a stereo output but they should be applied towards the end of a mix. Ideally, they should be used as sweeteners unless sound designing where the effects are being tightly controlled. Samples can be an array of combinations of stereo and mono signals but when using a synthesizer or any other modern sampling machine, you can create a mono output, just in case it suited the production.
The key with panning is to keep important drums centralized to ensure they are represented as expected. For instance, in house tracks, the kick and clap are the rhythm keepers and are, more often than not, kept primarily mono with perhaps just a sprinkle of stereo effects. In any case, the drum is essentially mono to ensure the important parts of the drum kits are heard, clearly every time.
If you were to pan one of the dominant drums in your rhythm section hard left or right, the energy of the rhythm section can become lost in certain acoustic environments. Imagine yourself at a concert or at a venue, the stage is relatively big. In most cases, it may take a good minute or two to walk from one side of the concert to the other, thus if you ended up on the wrong side at the wrong time, you may miss important parts of the rhythm because the drum was panned away from you. Keeping those drums in mono ensures that they will be represented evenly across all systems.
The nature of low and sub bass frequencies creates a surrounding-type feeling due to their unidirectional characteristics. Therefore, creating stereo movement will only harm a mix since the low frequencies cannot be detected very well in the stereo field. Hats are primarily high frequency and can exercise the stereo field with much more freedom due to their direct nature. They are far easier to hear and pinpoint within the stereo field.
Depending on how many drums involved in the rhythm section, you may need to pan far more than intended. The mono space should be occupied by the most important drums only and the rest may be panned as needed.
As a personal preference, keeping the drum kit equally wide on both sides helps not to skew a lop-side the image of a drum kit. For instance, if I pan a drum 15R, I will pan another element 15L to counter the movement. Using this method works well with instruments alike as they begin “talking” with one another.