Why are IUPAC names necessary?
Believe it or not, it is easier to have IUPAC rules/names than to name all compounds after someone/something or to give them nick-names. It would be confusing.
Why is that?
Because there are so many compounds and we want to know everything about some compound just by reading its name.
Formic acid (also called methanoic acid ) is the simplest carboxylic acid. Acetic acid, sytematically named ethanoic acid.
For convenience in communicating with other chemists.
For example, if one were to call the note A in music
Similarly, saying 2-propanone is giving a descriptive name to describe a ketone with three total carbons on it (hence "prop-"), as well as the middle carbon being part of the carbonyl group (hence "-one").
An exception to this is common names that chemists have used (also for convenience and for frequency of use).
"Hey, what's that compound you got there?"
"It's called Toluene."
"Wait, what compound?"
"In other words, it's methylbenzene."
"Oh, you mean benzene with a methyl group on it. Gotcha!"