Bit of a conundrum - blight spores are airborne, so in
theory the more airflow you provide, the greater the risk of copping it, although by doing so you would reduce the risk of botrytis which thrives on high humidity.
In practice, in over 10 years I've never had blight in the GH, although botrytis seems to be inevitable towards the end of the season, but it doesn't greatly affect the crop.
Removing any manky tomato leaves helps reduce the chances of botrytis getting a hold too early, and avoiding wetting the leaves when watering helps avoid both problems.