yeah, basically when you brake, the caliper will try and rotate the swing arm in the opposite direction to the wheel. Depending on the suspension design, this could either cause the suspension to compress, or to resist compression, neither of which are really desirable. It's very similar to how the relationship between the chainline and the main pivot can cause bikes to either bob, or lock out during pedalling. By having a floating brake, you i isolate all the braking forces from the suspension and feed them into the frame. This should leave the suspension to behave how it noramlly does. The other advantage of a floating brake is that it removes the forces of braking from the swingarm, reducing (to an extent, i'm not sure how much) wear on the pivots and bearings, and also possibly (i'd have to think about this a bit more when it's not 8:00 in the morning) reducing the torsional strain on the swing arm.