the jab

[donnydarkoIRL]

but can you think of any reason why you will need to jab with a weight transfer?

I suppose my first thought would be as a first phase in attacking the body.

believe it or not, you are only standing on one leg when you throw that jab: your front leg. to throw that jab, press down on your front foot and in the same motion swing over your back foot. you are looking for a smooth, break away action as you throw that jab, as though you are trying to discretely escape through an imaginary side door. the reason that you press down and anchor the front foot is so that you are able to free up the movement of the back foot. this is what gives you that break away action you want. but to do that, your jab must have a weight transfer onto your front leg, to both anchor your front foot and free up your back foot. properly done, and you will have placed yourself just a little outside his right shoulder. finding it very difficult to hit you there, he will turn, trying to position you back in front of him like someone pressing a return lever on a typewriter to put you back where he can hit you with his punches. jab that way again, and you will turn him again.

If the weight is placed entirely on the front leg, the boxer's lower body has no contribution;
the jab would be an arm punch and unable to generate the power seen in the jabs of Quartey, Lopez or Seldon for example.

The action you have described is useful when maneuvering out of tight angles, but would not work if you were on the offense or attempting to open up an attack by combination. It's a specific type of jab for a particular situation.

Traditionally the boxers fundamental position saw them with 60% of their weight on the rear leg, 40% on the fore.
Modern boxers have adopted a more balanced stance more suited to mobility, almost certainly benefiting from modern footwear.
In either era, boxers were not trained to carry their weight on their front leg, as this would see them 'leaning-into' the opponent's attack.

The most common method of teaching the jab sees the boxer pushing the lead foot forward simultaneously with the jab and then returning the lead foot to the fundamental position.
This allows the boxer to establish the jab, but retain their mobility.

Just my thoughts.