In an ideal world your bikes suspension would react differently every time, adapting to the road surface conditions and type of use they are receiving. The perfect spring would feature a top half that's supple, allowing them to react flexibly and absorb small bumps and irregularities, then as the spring compresses it would become more rigid so even large bumps and holes in the road surface wouldn't cause the suspension to bottom out. However in reality most bikes are fitted with 'linear' springs for cost-efficiency. This type of spring takes just as much force to compress the top half as it does the bottom half - resulting in a spring which is to rigid at the top and to supple at the bottom.