When locating a warehouse, there is usually a trade-off between the number of warehouses and service level. That is, as you add more warehouses, are you are closer to your customers.
However, if you can ship your product via air (like with UPS), there is a twist to this trade-off. You have the choice to pay for much more expensive air services, but you can avoid the extra cost of warehouses and inventory. For light, high-value items, it may make perfect sense to ship via air services.
I was able to publish a nice case study on this with Jim Morton (then of UPS). Click here for the article.