Finally, a thread about threads.

Silly question but just for discussion sake: I am bolting some safety chains
to our home-made trailer. Eventually they will be weled on as well as bolted
but for now (long story) we just want to bolt them.

So I got a 4" bolt in "Grade 8" hardened steel. But they come in both
course and fine thread. I went for the course thread. Question: Is there
any functional difference or reason to choose a course versus a fine
thread for this type (or other) applications??