Paul Randal hits us with another blast from the past:
One of the most fundamental concepts in any relational database management system (RDBMS), such as SQL Server, is the transaction. During my consulting career, I’ve seen many instances of performance problems caused by developers not understanding how transactions work in SQL Server, so in this tutorial, I’ll explain what transactions are and why they’re necessary, plus some details of how they work in SQL Server. There are nuances to some of this when Accelerated Database Recovery (ADR) is in use – topics for future articles.
One thing that Paul does not point out here but has done in other places is just how bad the implementation is for nested transactions in SQL Server. They’re very limited in nature, so the best advice there would be not to use them at all.