To buy or choose the level to cover depends on your asset, liability,
financial obligations, and expense. You would probably buy one to cover the
worst case scenario if you die prematurely, i.e. to cover any balance of
your mortgage, college expense if you kids may have, and living expense if
your spouse does not work.
In general, if you have young dependents, you should buy to at least cover
the worst case scenario. The younger you are the cheaper it gets.
If you are now 70-80 year old, the premium would be super expensive because
your likelihood of dying is high.