I don't think its ever okay, but as a manager, I could understand a situation that could push an employee to a point that they may need a bit of time to deal with things.
I think its the managements responsibility, to ensure that employee gets time to settle themselves, or are allowed to go home to deal with things, should they be trying to deal with death or anything of the sort.
What I do think is acceptable, are those using their tears to get what they want in a workplace.
They don't want to sweep floors. Out come the water works.
Customer returns a part that is wrong and you're tasked to fix it. Water works, until someone does the work for you, because you're too "distraught" to do it.
Emotional intelligence is a critical aspect of an employees skillset.
To me someone often rendered to tears, showcase often one who isn't very good at dealing with their job.