The big difference is that it can't be directly interfaced with devices that use 5v logic (nor even power them, since there's no 5v). The speed and pwm frequencies are also lower as noted above.
Make sure you use a 3.3v serial adapter, and if using serial adapter without the power line cut/disconnected, don't connect it to a battery when it's connected to serial (it doesn't have safe charging circuitry)