Lock Pages in Memory is a setting that can be set on 64-bit operating systems that essentially tell Windows not to swap out SQL Server memory to disk. By default, this setting is turned off on 64-bit systems, and depending on the circumstances, the following conditions could occur when this setting is not turned on:
1) Performance of SQL Server could suddenly decreases for no apparent reason.
2) The hardware running SQL Server could suddenly appear to stop responding for a short period of time.
3) Applications connected to SQL Server could time out.
4) Among many others.