The command is for Windows NT+ only. Lock volumes to prevent simultaneous access of the operating system.
If you edit not locked volume it may be damaged if another program or OS is writting to the volume too. Under Windows Vista/7 you can not edit the volume if it is not locked.
Close all programs which may use the volume before locking. The system volume can not be locked. Never try editing the system volume otherwise it will be damaged. Do not lock the volume where used program is located. A volume can be unlocked after closing.