sysdate vs systimestamp

In Oracle, the difference between sysdate and systimestamp is that

Sysdate is accurate to second.

Systimestamp is accurate to millisecond by default, and could be accurate to 1/1000 millisecond (Timestamp(9)).

It may make a big difference in a busy system. I had a project having batch uploading functions. The developer used sysdate for one timestamp column which was in a unique constraint. The sysdate caused a lot of problems.