From the KnowledgeBase
TSM: How to install on a Macintosh computer and backup your computer nightly
Back up often! To answer the question "How often should I back up my computer with TSM?" ask yourself "How much work am I willing to lose?" Almost all computer users suffer a loss of information on their computers at some point in their experience. This is usually caused by hardware failures, like a hard drive crash. To be prepared, you should back up your computer regularly.