I have a dumb question I should know, but don't.

I know on a dado, pocket, or cut out the the tool's diameter is taken into account, hence a lead on a through dado so you don't have rounded corners at the edge of your part. But if I apply a machining operation to say straight PLINE, is it the same? Do the start and stop of the tool path align with the outside diameter of the bit, or is it the center of the bit? I understand the offset/justification with left, right, and center, but what about length/distance?