What is the difference between bulkmarcimport and stage MARC records for import?

1. bulkmarcimport (BMI) is done through command-line whereas stage MARC records for import (SMRI) uses the web interface.
2. With BMI the records get cataloged directly so the reservoir step is skipped, contrary to what happens with SMRI.
   

So, given that, what's the intended use of the two functionality ? Being new to the library science field, I suspect that there is perhaps something more to the story than what I know.

BMI is usually used when migrating. So it's only once, before you go live. SMRI is used on a daily basis by librarians. For example after getting your order list from your book vendor you can easily import that list into the catalog without having to re-enter all of that information.