Mine doesn't have any effect on tone, but rather I find it a huge practical help:
Lehle 3@1 switcher
It makes guitar changes so easy: simply choose 3 guitars, plug them into it, pick up the one you want, step on the corresponding button & play. If you want to change, simply put it down, pick up one of the other guitars, step on the button etc etc. Live guitar changes are so much easier (& quieter!)
It has 2 outputs so you can plug in a tuner with no signal loss. Also, if you want to do A/B comparisons (say to compare different pickups :)) it's so much easier than having to unplug things.