Let me tell you few words on sacrifice branches. I use example of my Field Maple I was working recently (Acer campestre No.2). Reason behind unrestricted growth of some (one or more) branches on a tree is energy generation.
Imagine your tree is big growing City which needs a lot of energy for its occupants. It is modern Solar Power City. Branches of the tree are power cables. Closer to the trunk/city, thicker they must be to transfer energy(sugars). Leaves growing on branches are Solar Power Plants. If they receive sunshine, they produce energy(sugars). More sunshine means more energy. More energy produced by any single leave/(solar power plant), more capacity in cable(branch) connecting it to City(trunk) you need. So, when leaves on branch produce energy, they send it down, through the branch to trunk and roots. When Power Management Company (Tree) finds out branches produce more energy, than it is possible to transfer, it will send resources to thicken those parts of tree through which energy is transferred. So, Power Company people are adding more cables connecting leaves with trunk. It means all parts of tree structure between leaves and roots get thicker.
Now, how we can use this in tree design? We are able to thicken those parts of the tree, which needs to be thicker, due to our design plan. We can grow thicker trunks, and branches, where we need them (on lower parts of the Tree usually, but it depends). So generally, longer branches we get, more leaves are on them, and thicker they will grow. We need a lot of green foliage mass to thicken the branch or trunk. Do not cut leaves from sacrifice branch. Also, more vertical branch grows more energy due to gravitation is flowing through it. In case you want to thicken some specific branch, you can wire its tip into vertical position to strengthen energy flow.
We can also use sacrifice branches to help healing wounds on our tree. Obviously, there are trees which are able to heal cuts and wounds better (acer, quercus, tilia according to my experience) than others (hawthorns). But generally, more energy is flowing around cut or wound, faster is cambium creation around wound and healing is therefore faster.
Question is, how much sacrifice you have to sustain. This you have to find yourself. But I would say let it grow as much as you can, until you are sure cuts created when you cut it back will heal. It is easier said than done.
So, back to my field maple. It was not cut back this season up until last weekend. You can see the pictures with amount of growth produced by yourself. Now tree, was cut back. Cuts were worked a bit. Majority of branches were wired. It will stay like this for couple of weeks before wires start to bite in, they will be removed. If you check previous post about this maple, last year I did more less the same. This is, according to my experience, way of building deciduous bonsai from yamadori collected material.
|man behind the tree|
|...5 minutes later|
|One of the major wounds, with maple one can at least hope it will heal in couple of years of aggressive growth of the crown.|
|2016 and 2017 same wound, more growth, more callus, faster healing|