Fungi are natural decomposers in ecosystems. They break down waste and dead organisms, and return the nutrients back into the ecosystem so more plants can receive nutrients, animals can eat those plants, and so on and so forth.
If all the fungi died out, things that decompose it will remain, and the nutrients will not return to the ecosystem. This will cause the plants to receive less nutrients, along with the animals, and as the cycle continues plants will not have enough nutrients to become a sustainable food source. If this happened, the herbivores would not have food and die out. The creatures that eat the herbivores would not have their food either. Eventually us humans will not have good food sources due to lack of nutrients.
In terms of the economy, many animals are sold in the stock market or sent to stores for humans to buy. If there was a large decrease in cattle, for example, the cattle stock would disappear and all the shares in that stock would be lost. This would make a lot of problems, and as the stock market is very complicated and large scale it would be an absolute disaster if an entire stock disappeared. It also wouldn't be JUST cattle. Wheat, corn, and crop stocks would be lost too. Other animal or livestock stocks would be lost as well. This could eventually cause the stock market to crash in a way, which would lead to the Great Depression. Just because of fungicide.
It's not like you would put down some fungicide and the stock market would crash a month later. It would be a very slow and gradual thing, which is good so we can keep things like that from happening right now!
The biggest advantage is that they have a higher resolution and are therefore also able of a higher magnification (up to 2 million times). Light microscopes can show a useful magnification only up to 1000-2000 times. This is a physical limit imposed by the wavelength of the light.
