So let's say we have a web application for an autoshop.
The employees use this application to keep track of cars and other related work as it moves from checkin to diagnosis to repair, and then back to the customer for billing.
The customers use this application to check on the status of their cars, request extra servicing, and get an invoice for the work performed.
Also, the autoshop doesn't do everything right in house, and has a few specialty contractors in the areas. Sometimes a part or an entire vehicle will be shipped off to a contractor for a few days before finally being returned for final repairs. The contractors also use this application to be alerted of new jobs available for them (they have to go by and pick up cars every morning), make notes on how the repairs are coming, and then mark down that the cars are done and should be returned.
Three very distinct groups of people use the application for different but related things. The employees can see most data in the system, but the customers should only see things relating to their account, and the contractors should only see things about the cars currently and previously assigned to them. All of them need to be able to access the application from anywhere.
I'm wondering, would it be a good or bad idea to treat this as one application with one url, which, depending on the user permissions, takes them each to a very different section of the site? Or are there issues I haven't thought of?
Update: For people thinking about permissions/authorization, I should mention that this application becomes more complicated in that regard. This autoshop also handles fleet maintenance for a few companies, and thus a single customer may have multiple logins associated with it: the accounting office has one login that lets them only see invoices, where as a different office can only see the repair/maintenance reports, and should not be able to see invoices.
Contractors have a similar set of special authorization rules.