I understand, it makes sense. I would definitely check in a bag if what I wanted to take did not fit in a carry on or if a trip was over a week. But, what is the point of checking in a bag if it all fits nicely in your carry on?. Added risk (especially in some third world countries), time wasted, etc.

The issue here is when you are slightly (a few pounds) overweight with your carry on. It only applies to a few airlines that have very restrictive weight guidelines. You definitely want to avoid having to check it at the gate when unprepared to do so, or having to shuffle stuff around at the last minute.

This does not apply to 95% of airlines out there. It only applies when you are on a long enough business (or not) trip (say a week) where you can definitely do it in a carry on, but have to fly these airlines and you know you might be overweight. I've noticed people seem to get very stressed and angry when they have their luggage denied boarding because of a few pounds.