The Bridge Removal indeed refers to the brigde across the main bearing.
To understand why this has a sonic effect, one should know that the bearings are preloaded very high with SME IV,V,309 tonearms (and their siblings). And then the vertical bearing is very sensitive sonically, a lot more than than the horizontal bearing, in my experience. If you remove this bridge, you lower the preload, and thus gain treble air and lose some harshness. But, at the same time, you lose some bass power. From what I have tried, it is best to losen the screws of the bridge, then retighten it again. With this you lower the preload, but don't lose much bass power.
best regards, Hartmut