Well designed load carrying bikes like touring bikes, will be heavier to better deal with the loads on them .
the frame made more rigid, by increasing the tube wall thickness/diameter, in higher strength steel or aluminum alloys.
A frame made with low cost steel will use more steel to make it strong enough , a high tensile strength alloy steel
will be sufficiently strong with Less .
if not in a hurry , like in Racing, by lowering the gear ratio, heavy, eg Touring loads, get up hill in a reasonable time period..
Lighter bikes will go faster for the same effort. How much faster, and at what price are the questions most debated.
Overcoming air resistance .. the guy on the saddle is most of the air resistance ..
bike parts weight and aero stuff is about the last 2%
like to ride all day bent over, as low as you can? is that comfortable? not to me..