Fungus and bacteria are important elements for creating a healthy soil and for decomposing compost into plant available nutrients. Various fungal organisms are closely associated with plant roots, essentially extending the plants root system into the surrounding soil. Thus more nutrients are available to the plant. This relationship greatly benefits my vegetable gardens and orchards, allowing me to avoid using commercial fertilizers.
There are plenty of other benefits to having a healthy population of fungi in the gardens...
...fungal filaments bind soil particles, creating better porosity
...plant roots grow better in the presence of beneficial soil fungi
...soil fungus helps suppress soil pathogens (the bad guys), thus keeping plants healthier
...healthy fungal colonies help plants deal with drought and root diseases
...fungus breaks down woody material, a much appreciated activity in my growing areas.
Research says that fungi can also be used to treat contaminated soils.....a process called bioremediation. I'm seeing a number of professional research papers available on the Internet concerning various types of fungi vs contamination. Very interesting.
Perhaps D's mother removed mushrooms because she feared that her children might eat them. Many garden mushrooms can be toxic to humans.