I don't know what kind of concessions, if any, come to the producers/theatre owners by doing this, but, looking back at the Sister Act grosses from the same time, they were able to maintain their Gross to Potential and their Avg Ticket actually price increased slightly jumping up by $5 through October.
Fiddler has also adjusted their pricing structure to coincide with with the curtain closing. Their least expensive regular price option jumps to $49 from $35, While the top price drops from $147 to $140 tot he performances with the curtain closed. Weekends are currently listed at $49-$157. So Fiddler is probably hoping to sell about the same amount of seats at a slightly higher average price point to maintain their numbers through the slow season, and ahead of the holidays/closing, when they will undoubtedly do significantly better than the slow months.