Advantages? I'm not sure what you're trying to ask in this question. The usefulness of them are vast, we often eat their left overs, Beer, Cheese, Yogurt, the list could go on, all use bacteria to make them. Our digestive system also uses them to help us digest our food. However there are downsides to many as well, illnesses are often cause by some of them. So you have good and bad microorganisms.
In detail? Do you have any idea how many microorganisms there are? No one can answer you in detail without spending hours.
Cliff notes version...some are good and some are bad, but few think of those tiny little things that don't get seen by the naked eye. For instance, you have good ones on your skin and using anti-bacterial soap kills them, when you need them. Balance and order in nature, in the human body, in all living things have these microscopic things hanging out... If you want detail, be specific on which organisms, on what living thing, regarding what kinds of outcome.
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