Why do you take leaves off a plant when cloning it ?

Are you talking about taking leaves off the mother plant or the clipping (the daughter)?

the clipping:)

Well, that’s interesting because when you’re cloning a plant, you don’t want to take all the leaves off. You should take the lower leaves off, which will keep them out of the water/rooting medium, but you want a few near the top to aid growth.

2) Locate some older, lower branches with about 4–6 sets of leaves on them, and that are about 1/8–¼-inches-wide and 3–8 inches long. With your scissors, make a 45 degree cut across the intended clones branch, being careful not to smash the stem. Trim the 2–3 sets of bottom leaves off the stem, leaving 2–3 sets of leaves above ground. Immediately place the cut end into the glass of fresh, tepid water. This will keep an air bubble from blocking it’s transpiration passages, which can kill a plant within 24 hours. Leave your cuttings overnight in the water with no light. (link)

Place the stem on the sterile cutting block and slice it at an angle of 45°, around ¼ inch below the leaf nodes. Take care not to bruise or crush the stem while handling. The plant cutting for cloning must contain one or two leaf nodes and leaves and must be around two to four inches in length. (link)

i don’t know the science behind it – but i’ve made jillions of clones.

i cut the leaves off (and nick the node) to get roots to come out (and usually the leaves fall off anyways). it helps the plant focus on re-rooting (and not keeping the dying leaves alive).