White residue comes from too much being applied to one area. As a theoretical example, say that every square inch of skin can absorb, at the max, 1/10 mililiter of gel and you have to apply 5 ml. So, you'd need to apply it to 50 square inches of skin. If you only used 40 then it all would not be absorbed properly and you'd get the residue.
This is a real basic version but you get the drift I'm sure.
Also, by maximizing the area you are also maximizing the efficiency of the dose. At one time I had to restrict my gel to a single area of the body and my T levels actually ended up dropping to BELOW pre-TRT levels!!! Why? Because the skin was saturated and couldn't absorb any more. The rest just flaked off in the form of that white residue.