I couldn't figure out the effects of strut offsetting, but on several cars such as air-cooled Porcshe 911s or Ford Focus WR cars you'll find such offset. I am a big fan of the steer feel of BMW 3 series, well known as high caster angle car and, as you can see, the strut and spindle of the car are obviously at offset position from the king pin axis. Thus, even though strut offsetting appears to be weird, I guess there is no practical side effect.