Speaker Cables, One side longer- bad idea?

If you have a stereo amplifier where each channel has a common ground, than you most likely will increase an inter-channel noise and distortions since different length cables have different resistance, capacity and inductance. Stereo amplifier has to be equally loaded -- it's almost like you will plug in different speakers to each channel. In dual-mono amplifier or monoblocks you will have on the shorter side slightly better details than on the longer side. This difference you will not be able to rectify with channel ballance if the one is present in your preamp.

There won't be an audible (probably not even measurable) difference with the lengths you mention. Marakanetz's comments are correct in theory, but you would only need to worry if the 2 sides were really different. I asked this question of a well-known cable maker/designer (really nice guy) at a show a few years ago and his explanation left me with the conviction that a 1.5 to 1 ratio or less should be fine. OTOH, a dealer I know has done blind tests with 5 and 1 meter runs of a mid-priced high end cable and none of his sophisticated customers have been able to tell a difference in sound.

If someone wants to illustrate the difference with numbers, that might be interesting.

Keep them equal so the cable characteristics are matched electrically and sonically.