Importance of database transactions

If you were writing a tiny app for yourself that only you were using, it's arguable that database transactions are a needless overhead. However, in an environment such as the Web, where multiple users are likely accessing the same data at the same time while data manipulations are occurring, database transactions are a good thing. You want your data to be consistent and valid. For without database transactions, a system under heavy use would lose all data integrity before you finished reading this sentence. I may or may not know this first hand.