A lot of masters are simple cash cows, targeting either native workshy students or internationals who don't understand that the qualification is essentially meaningless.
However in some fields qualification inflation is so bad that a masters degree is a pre-requisite; also, you will find that if you intend to work in Europe masters degrees are the norm over there. The other time a masters is useful is when you want to demonstrate commitment to a different field from your undergraduate degree, which after all you decided as a naive 17-ye