I've given our grape vine that the previous owners had planted in the greenhouse a haircut. It gets a hard prune in winter, and we also prune it throughout the growing season as well.
The first year we were here we didnt prune during summer, and ended up with disease on the fruit. We haven't had any problems since by pruning some of the leaves off to open the vine up to allow airflow through. Being in the greenhouse it gets super duper hot and humid of course, which fungal diseases thrive in. Hopefully we get a bumper crop again this year!