If you want to used their service and comfortable with that, I don't see any wrong using Coinbase. But again, like others mentioned here, Coinbase is an exchange wallet meaning you are entrusting your coins to them. So in case that something wrong happened, there are chances that you will be fu**** up. Coinbase is a big company and running for several years now but it doesn't mean we need to trust our coins to them at 100%.

Again if you are comfortable with their service other than other exchange then:

For holding purposes:
-Buy Bitcoin at Coinbase
-Transfer it immediately in wallet where you control your own keys. Desktop wallet will do.

For trading purposes:
-Buy Bitcoin at Coinbase
-Transfer it to exchange
or
-Learn the deposit method of a certain trading exchange then do the deposit here to save fees.