To put it simply, Word Work is an added feature. It is there to supplement the learner's training alongside Courses. Users can interact with the Word Lists in the Play section. They can go to Play > Select Content > Word Work
Then the words will be used in the activities in Play. It's useful when you want to practice typing your preferred words/vocabulary. Or learn and be familiar with those words in a typing situation.
Users can easily go to Word Work to learn about words. It has access to Wikipedia and Wiktionary. See, with good vocabulary, users can read and type the words easily because they're familiar with it. They've mastered it. No need for the brain to stop and ponder what the word means thus slowing down reading/typing.
Typesy does not require you to use this part of the program but it definitely is an option - a supplement. Not all users find it necessary but it's available. You can use it at your convenience.