As an all-grain brewer, 90 minute boils are good for high gravity beers. We can sparge with more water, collect more wort, and then boil longer to compensate. This improves our extract efficiency on beers where it would otherwise be poor. The only expense is the extra 30-35 minutes, and an extra half gallon of water.
For an extract brewer, there isn't much point to a 90 minute boil. I would definitely advocate adding most or all of your extract late in the boil to increase your hop utilization. But ya, a 90 minute boil isn't doing anything for you.