That depends greatly on the bow itself and how much vibration it was generating . On my recurve it made a noticeable difference . I have four of them on it .
I actually just conducted a test with LimbSavers, adding just about everything they sell to a bow. I couldn't believe the amount of vibration it reduced, I would say the more the merrier!!
I know I have one set on my bow, plus an s-coil stabilizer, but my bow is still pretty noisey. I might just have to try this idea for multiple sets of limbsavers.
The guy I e-mailed at Limbsaver said that more limbsavers would dampen more vibration, but any more than 2 sets (4 total) wouldn't be noticable to you or I.