Suppose that configured Timeout for server is less that Timeout for agent
We have an zabbix (passive) item with the type "Character" and it's an UserParameter which sometimes spends more time than agent allows (Timeout).

In this case agent returns the value as "timeout while executing a shell script" and it will be as usual written to DB instead of generating some sort of error like NOT_SUPPORTED or TIMEOUT or so.

This behavior can be unexpected to end user and it's not so easy to note those moments.