Stepped allows you to gradually open a hole up to the size you want instead of starting with smaller drill bits and having to change to larger bits. It just makes drilling larger holes much quicker.And yes, it keeps you from tearing or distorting the sheetmetal you are trying to drill the hole into.
A "steped drill bit" Could be two different things A uni bit withe several different sizes or a steped drill bit with two different sizes (for more percise holes).
Both are used for the same general thing. Have you ever tried to drill a hole with a .250" (1/4"
or larger drill bit well you probably noticed its hard to locate the dead nutz center of your mark the larger drill bit wants to find its own place to start the hole. now the opposite is true with a smaller drill bit. the uni bit works good cuz you only chuck up twice (dont start the hole with a uni bit). Chris