Of course, the benefits vary depending on who your platinum credit card is with, but most of the time you have a larger credit line, better rewards programs and can get discounts with various companies when you use the card.
Generally, platinum cards offer high/no credit limits, often a percentage-back bonus system, sometimes lower interest rates, and occasionally special discounts or offers with affiliate companies.
The main benifits of a platinum credit card is that it is accepted in many places that the average credit card is not. For example if you travel you would have a much easier time using it.