MSTDC is used for distributed transaction. To simplify, using a TransactionScope can implicitely use MSDTC if the transaction needs to be distributed, ie: if the TransactionScope surrounds a piece of code that implies more than one resource. This is called escalation, and most of the time happens automatically.

So, yes it takes somes resources, but if you do need ACID transaction across multiple systems ("resource managers", like SQL Server, Oracle, or MSMQ for example) on a Windows OS, you don't have much choice but use MSDTC.

One thing about performance that can be done when configuration MSDTC, is ensure there is only one Coordinator for a pool of distributed resources, avoiding MSDTC to MSDTC communication. Configuration is usually the biggest problem you'll face with MSDTC. Example here: http://yrushka.com/index.php/security/configure-msdtc-for-distributed-transactions/