Consider multiple processes are accessing a set of frequently updating records and they pick whatever matches certain criteria. They should lock those picked up records. So almost at the same time if any other process wants to pick their share, they should skip the locked ones, rather search for only new records that are not locked.
To lock records, we append
For Update at the end of SOQL. So while a process is working now with such implementation strategy, what other processes would do pick other records skipping the locked ones?