Do we need to keep time on application servers synchronized?

Question:
HI, all:
The time on each of the 3 application servers in out production system were only synchronized manually maybe once a month. Thus, most of the time, there is a difference among the time on the 3 servers(HP-UX, Oracle 9, SAP 4.6C). The system seems to be operating OK even the time are not synchronized. I am just curious whether this time difference between each app servers matters or not? Thanks.
Answer:
It is among the best-practice recommendations..

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