I find accuracy helps with speed as I'm not having to back space all the time or go back through using the spell checker when I could have had the word typed right the first time without the common mistakes.
I think if you're just starting out trying to learn to type fast, focus on your accuracy. I have a friend who has played over 1.1k games on here who just focuses on raw speed and hasn't improved much. Focus on accuracy, and speed will eventually come along the more you practice.
Accuracy IS speed. Imagine you're driving a car. Will you arrive faster at your destination if you floor the gas pedal but keep taking all the wrong exits, or if you keep a steady pace and take the correct route? Speed is not how fast your fingers move (that may be dexterity, but not speed), speed is how little time it takes you to type the words without mistakes.
It it fundamental to focus on accuracy, as it allows you to type more comfortably (and this will automatically improve your speed, because if you feel more confident with the way you type, you gradually increase your speed more and more). From my own experience, I have practiced accuracy for weeks now and I can say it's totally changed the way I type as I know better where the keys are.