Ryan Adams gives us the skinny on the Microsoft Distributed Transaction Coordinator:
MSDTC configuration is not as straight forward as you might think. It’s a different choice if you are using a local MSDTC, clustered MSDTC, on-premises, Azure, Failover Cluster, or Availability Group. Every one of those variables leads you down a different path with different choices. The goal of this article is to clarify those choices.
If you think you do not use the MSDTC, you better check again. I frequently see folks using it that do not realize it. The most common is Linked Servers. You got it. If you are using Linked Servers, you’re using the MSDTC.
You are no longer required to install an MSDTC with a SQL Failover Cluster starting in SQL Server 2008. That does not mean you do not need an MSDTC configuration. If you wanted to make your application database highly available, but your application did not use the MSDTC you were being required to install one anyway. That limitation is what was removed, not that you simply didn’t need a clustered MSDTC.
Read the whole thing.