As stated in the title, the question "What are the advantages" is translated into "cosa sono i vantaggi" even though "cosa" is singular for "things" and the plural should be "cose", as far as I am aware of.
Cosa is (or, better, is used as) an interrogative pronoun, so it doesn't agree with the subject of the sentence in which it appears. So we say Cos'è un carciofo? (“What is an artichoke?”), Cos'è una penna? (“What is a pen?”), Cosa sono le Erinni? (“What are Erinyes?”), and so on.
Actually, the complete expression would be che cosa (literally, something like “which thing”). So one asks, more or less, “which thing is an artichoke?” and the like, independently of the gender of the thing asked about.
However, if you already know what a pen is, but are asking which out of a jumble of pencils, markers, and other similar stationery items is the pen, in Italian you'll ask qual è la penna?
For more about che, cosa, and che cosa, see a previous question.