That's exactly it. There's only two or three throttle settings, or the engine can be "blipped" (shut down and restarted repeatedly). The benefit of a rotary though is that unlike an inline, it doesn't need to warm up- its ready to go as soon as its started and running smooth. That's why you see the period footage of planes like the DR.I starting up and immediately rolling away and taking off- as soon as its smoothed out, you're ready to go.
Downside though is that it's lubricated with castor oil and that the fast spinning engine is constantly throwing out into the slipstream. One explanation for both the scarf wrapped around the lower face and the sickly looking pilots from WWI is the constant ingestion of Castor Oil- the scarf to keep it out, and the stomach problems caused by swallowing it by the quart.