Beginner typing is a discrete muscle action, under conscious control and attention. Hunt for, or try to remember, where the letter is. Then the finger moves a fixed amount and hits a button. Then the next letter. Sort of jerky. Letter by letter. Fluent typing is a more composite act, a sort of dance where the fingers roll back and forth in extended, fluid motions. Not coincidentally, fluent typists are prone to mixing up words like "fluid" and "fluent", as I just did and had to correct. Type entire words or phrases correctly, incorrectly. Often they sound similar or have a similar semantic sense. Slightly fuzzy erroneous activation, of ingrained muscle memory patterns, is my interpretation of that effect.

A similar level of fluency emerges with handwriting over time. One stops forming individual letters, and whole sequences become one extended flow of the pen. Entire words. It detaches the executive function and short term memory and attention of the mind, from the flow of individual letters and how words are spelled and put together. That becomes an automatic process.

We probably wish to encourage that fluency in multiple modes.