I shall presume you are referring to suspension bushings.
They may be more complicated than they look. The first concept with a bushing is its ability to act as a pivot point. Other pivot points include: ball and socket and trunnion/shaft arrangements. The ball and socket are obvious, and trunnions are for the 108 crowd, but bushings are much of what we currently use.
The suspension link will need to pivot on the attaching axis. The link is steel or aluminum and the bushing will be pressed in. (sometimes made in). The typical bushing is a steel inner cylinder surrounded by the rubber which is encased in the second steel cylinder. The outer is pressed into the link and the inner is pinched hard by the attaching hardware. The ABILITY to pivot is totally in the flexibility of the rubber as all metal components are FIXED. Think about this. The metal inner hole does NOT move, as it is firmly attached to the frame (etc.).
The reason they use this method of pivoting and not ball joints or trunnions is partially cost but mostly for noise dampening. All the road noise coming through the suspension has to be dampened in the subframe or your posterior. The noise from different aggregate pavement and tire noise is the level of dampening to be dealt with. Many of your suspension upgrades include some form of stiffening to the bushing or replacement with ball joint type pivots. The point is to limit the alignment change that occur during heavy loading due to the flexing of the rubber pivot (bushing).
The problem with the hard plastic bushings is that they have no way of performing the flexible pivot function and wind up squeaking and knocking during flexing. Hime type joint (ball joints) provide and excellent suspension for racing but let all the road and tire noise through. It is a design question best left to MB IMHO.
Bosch Master, ASE Master, L1
33 years MB technician