ExpressRoute is an Azure service from Microsoft allowing you to create a direct, private, connection between your local infrastructure and all the services available from the Azure Cloud.
For example, with the cost of local storage spiralling it could make sense to put this in the Cloud and access remotely.
You may require multiple sites to all access the services directly, or be happy for a single connection to be provided to one of your offices and services accessed from there.
The main drivers behind implementing ExpressRoute are: