I used to wonder what they were for too but I have suddenly realised their use.. I have two Warwick Infinity's that are amazing to play due to the lack of space between the strings and body. I never realised how much easier it is (for me anyway) to play, especially percussive techniques when there is this minimal space.I have a bolt-on Thumb which has loads of height and I pretty much find it unplayable now because of this.