There are several practical reasons to have multiple e-mail accounts.
- Separate business and personal email
- Redundancy in case one service goes down.
- Prioritize messages -- such as having an account for important stuff and others for newsletters, etc.
- Having an account for mobile device so that it isn't choked with newsletters and HTML messages.
- Increased storage space.
- Exploring what's out there. What kind of services are available and how do they work.
- Need for own domain services to host MX records.