It plays a large part in certain aspects such as mining. As far as I know it's never contributed to one line of Bitcoin's development.

As for trading, when it had zero fee exchanges people believed that 98% of trading volume happened there. In reality it was few bots throwing the same coins at each other thousands of times a second. When the exchanges were shut down and reopened with fees then we got a realistic impression.

It's significant but not the be all and end all.

https://coinmarketcap.com/currencies/bitcoin/#markets