Which is known as pan width. But that isn't true stereo width as there are not distinctive phases coming from one sound.
So when you play one kick sample in the center it will always be there coming from one direction were as if you use stereo the sound will have a nice depth to it and will imitate the way we humans actual hear.
***Stereo sound systems can be divided into two forms: the first is "true" or "natural" stereo in which a live sound is captured, with any natural reverberation or ambience present, by an array of microphones. The signal is then reproduced over multiple loudspeakers to recreate, as closely as possible, the live sound.
Secondly "artificial" or "pan-pot" stereo, in which a single-channel (mono) sound is reproduced over multiple loudspeakers. By varying the relative amplitude of the signal sent to each speaker an artificial direction (relative to the listener) can be suggested. The control which is used to vary this relative amplitude of the signal is known as a "pan-pot" (panoramic potentiometer). By combining multiple "pan-potted" mono signals together, a complete, yet entirely artificial, sound field can be created.***
iZotope has a nice visual representation of this in thier Stereo Imaging plugin.