In order to understand the importance of SQL Server backup and restore, imagine a situation in which one of your colleagues creates a SQL statement without a WHERE clause and executes it. The result of this is all the data is wiped off.
If your SQL Server transaction log (LDF) file is too big – you are doing something wrong. As technet puts it:
Typically, truncation occurs automatically under the simple recovery model when database is backed up and under the full recovery model when the transaction log is backed up. However, truncation can be delayed by a number of factors. For more information, see Factors That Can Delay Log Truncation.