Palash,
I did not say its not a common practice to lock/unlock before/after database update - On the contrary, I pointed out that common sense should prevail before and after a programmatic database update. Lock and unlock are not mandatory but they are just good practices - programs still compile correctly if someone did not lock/unlock before database updates...hence it is not "mandatory".
But I still do not understand why a SAP standard table is directly written to via direct insert/modify statements. Is that a "common practice" too?
Sougata.