As must be obvious to anyone who gives it more than a moment's thought, if you keep increasing the percentage of your weight that you move from one foot to the other, eventually you'll be transferring all of your weight, or 50% if you figure that the starting point is equal distribution. Either way the result is that one foot will be supporting all of your weight and the other supporting none, not even its own.
(You might wonder what the big deal is, since we all do this every time we walk. Walking is automatic behavior, something our skeletons are designed for and our neural systems are predisposed to learn. Moving sideways is at least less so on both counts.)
To be quite truthful, even this state (complete unweighting) is not the end point of weight transfer, but merely a plateau, one you may not ever feel the need to progress beyond. What lies beyond is transferring weight not just linearly, between one foot and the other, but transferring it in time, and between force and momentum.
While you mull that over, let's get back to the plateau state, where all your weight is supported by one foot and none on the other. One thing you will quickly notice is that it suddenly becomes much harder to maintain your balance. This is because, instead of using small forces on a long lever (the distance between your knees), you are now having to use larger forces on a much smaller lever (the distance across a single knee). This increase in difficulty happens as the last few ounces of weight are removed from the unweighted foot, so let's put them back onto it for the time being, just enough to allow you to keep your balance without putting extra strain on the knee that's already supporting very nearly your entire weight.
You can use the ball of your unweighted foot, or leave it flat on the ground, or pull your toes back and use the heel, and it's best to try all three. While moving your weight back and forth you'll want to slow that movement so it comes to a stop, pauses briefly, and reverses just short of a complete transfer. Occasionally you'll overshoot and your unweighted foot will lose contact with the ground while the opposite knee complains about the sudden increase in strain. For this reason it's best to start out with something solid in front of you that you can hold onto or grab quickly when needed. A horizontal bar attached to a wall at about elbow height works well for this. If you're practicing outside, you might also try a pair of ski poles, with their points planted in line with or slightly behind your heels, and about two feet further apart. (Placing the points in front of your feet may cause you to fall backwards if you need to make use of the ski poles.) In urban areas, you may be able to find guardrails along sidewalks made from welded pipe; these are ideal.
This is the first fully reciprocal exercise. The end of the movement in one direction blends into the beginning of the movement in the other direction. These reciprocal exercises are an important feature of the practice I'm describing here, and there will be more of them.