"Total Eclipse can automatically recognize prefixes and suffixes even when tucked into the same stroke as an existing word. Fewer strokes mean faster writing and less fatigue."
It just means if your final G (-G) means your -ing ending, then you can stroke it with your last stroke of a word and not have to come back and hit G by itself.
So HIGT would be hitting unless HIGT is already in your dictionary for some other word. So it's now one stroke instead of two, HIT/G.