If you have real Stereo samples, there are several situations that make them stereo.
a. They were recorded with two microphones equidistant and separated by at least 1 or 1.5 meters.
b. One was recorded from where the sound was made, and the other from a different place. // For guitar: one microphone is in front of the sound hole and the other is in the middle of the neck.
c. One microphone was close and the other far-away.
It is not recommended to set them as "-50/50" or exactly "L/R", except for the "a" option.
Because in option "b": sound-hole/neck-sound mix will be made. // A value like "-12/12" or "-6/6" might hold this better.
In the "c" option, it is aimed to adjust the far-near (timbre) setting. By increasing the attenuation of the near microphone and decreasing that of the other, it can be made to sound farther and vice versa. This setting adjusts the distance to the stage. With the L/R option here, it allows to adjust the right/left position of the place we stand in the hall in 3D.
If both samples are exactly the same, then we cannot talk about stereo. There are two identical mono samples and it has no effect on stereo.
In any case, the aim is to trick the brain in line with the desired purpose by giving different samples to the ear. : eg: a sound to the far right, whether the place where we listen to the guitar is near the sound hole or the handle, the sound reflection and absorption properties of the hall walls are different compared to the place where we listen in the hall, etc. This is why stereo samples sound fuller.
Of course, it is also possible to ignore all the parameters of the auditorium, use the instruments as mono, and adjust and pan the other necessary effects externally during mixing.