On most farms, mastitis is most common at calving and in early lactation, so any effort to reduce the risk of new mastitis infections around calving is likely to be well rewarded, as long as the efforts are properly targeted and well done.
Even though drying-off is a very important part of preventing new infections at calving, there are still significant opportunities to manage the calving period (2 weeks before calving until 2 weeks after calving for each cow) to further reduce the risk of new mastitis infections.
Every new infection at or around calving has a strong chance of becoming a chronic infection until we get another opportunity at drying-off to remove that infection, so this is surely a time where "an ounce of prevention is better than a pound of cure".
And how depressing is it to see a well bred freshly calved heifer that you have spent a lot of time and money to rear to this point, only to see her come into the herd with mastitis, or develop it shortly after calving?