Pay vs pay off

Hi,

I was wondering does it make any difference whether I say 'it pays' or 'it pays off' ? I approached both forms and despite doing some 'research' can't see the difference. Or maybe they are interchangable?

According to my Collins dictionary:

If a course of action pays, it results in some advantage or benefit for you.
It pays to invest in protective clothing...

If an action pays off, it is successful or profitable after a period of time.
Sandra was determined to become a doctor and her persistence paid off.

Does this mean that we distiguish them according to the time after which they bring some profit? I didn't notice such distinction in other dictionaries.

Can anyone, please, explain it? Because I know it's going to bother me..

Thank you, Justyna