A perfect example is that the greenest modern computers today are Macbooks and Macbook Pros. These computers are hardly inexpensive - they're actually some of the most expensive computers in the market.
Furthermore, some computers that are green may be considerably underpowered. Some people may need incredibly power-consuming and powerful computers to deal with the tasks that they need them to do. This is another disadvantage that many people who have high-powered computers believe to have with green computers.
Another issue would be that powerful and green computers are more expensive. For instance, Apple's powerful range of computers, including their iMacs, are incredibly green but are also incredibly expensive.
By conserving resources, it means that less energy is required to go about producing, using and disposing certain products so this is naturally a huge benefit. Saving energy and resources can actually save people money in the long run.