Why Evolve Technology Anyway?

A solid question to explore is "why continuely build and expand technology that already efficiently achieves the desired end?" Let's step out of the device paradigm world and look at a simple technological advancement. Stone to metal. Stone certainly was readily available, and capable of being crafted into a variety of tools to achieve survival, now this example seems obivous. Well, obviously metal is sharper and stronger, but then why use iron instead of bronze? Well, obviously iron is stronger and sharper than bronze. Ahh... Well, if we continue this incremental advancement eventually we hit a point where the technological device reaches a local maximum of efficency, effectivness, availablity, etc. That logical reshaping of the device to continually strenght its qaulity and effectiveness seems only reasonable for a, say, tribal society trying to maximize their hunt. But this incremental advancement isn't always so clear, or simply and advancement to beter achieve a desireed end. Lets look a the telephone, At first it was very localized, then grew in distance, and grew in sound quality, and microphone qaulity... Each one of these incremental steps seems obvious, just like the arrowhead, of why you would improve upon. At what point does an advancement or change become unnecessary and just advancement for the sake of advancement? For the telephone, the jump from phone to camera/phone is hard to directly see how, having a camera somehow enhances the conversation over the phone? Sometimes advancements become unnecessary, take the baby monitor, is it NECESSARY to have a hand held LCD 3 way communication ifra-red video montior to watch your baby sleep? Why do we keep just addin' more and more techno-perks to products that their grandfatherly ancestors achieved at the same level of effecitveness?