Companies don’t always have high availability. What’s more, there is always a concern of budget and complexity with the high availability even though a number of factors need to be considered during network design.
If the applications of the company do not require high availability, dual carrier or two links to the same carrier is not necessary.
Multihoming refers to a connection to the two different carriers/service providers even though two routers via two links to the same provider is not considered multihomed.
Dual carrier also refers to two different service providers that do not use same fiber infrastructure, Point of Presence (POP), and data center. This is important for the overall availability, and it is also known as fate sharing in the networking.
To choose between single carrier and dual carrier connection, there are more factors apart from budget and complexity to be considered.
The comparison chart below provides excellent comparison for single and dual carrier design choice for companies. In sum, companies should use this chart for their decision process.