A lot of fitness is about contractions - you're doing squats, or you're on a bike and your knees are bending but never stretching all the way, so your muscles get strengthened but look short and thick.

Contractions, 'U' for 'you' and the like are wonderful to make communication brief and efficient - but we wouldn't want all our talk to be only brief and efficient. Taking pauses out of language would be like taking the net away from a tennis game. Where would all the fun go?