Care should be taken that open files are always locked for certain groups of users. In addition to this, they occupy memory space and the copy on the disk is not consistent. Therefore, it is advisable to close the file as soon as it is no longer needed. This should not, however, result in otherwise superfluous OPEN calls. In the case of tape files, CLOSE involves rewinding the tape, which blocks further access to the drive concerned for some time. Consequently it is advisable to issue the call in time to prevent subsequent operations from being obstructed.
If the contents of the file have been reduced considerably and if they are likely to remain small for a long time, then its size should be reduced after the execution of CLOSE by means of /MODIFY-FILE-ATTRIBUTES (operand SPACE=*RELEASE(...) given) or FILE macro with a negative value for the SPACE parameter.