use of peat moss in the garden
Peat moss comes from ancient peat bogs and is not a renewable resource. For this reason, among others, there is concern about using it up.
It has been used in home horticulture, like many other biodegradable soil amendments, because it lightens soils (let's air and water in) with its big particles. Here is more about peat moss from our website, including how it fits into the bigger picture in home horticulture: http://extension.umd.edu/hgic/containers-and-growing-medium-seed-starting
Peat moss is acidic (low pH) which has made it a favorite of use with blueberry and other acid-loving plants. But, there are other ways to lower pH when that is necessary. There are many other soil amendments (including homemade compost) which will serve the same purposes as peat moss.