I currently have a few trees that do not look very refined. As a matter of fact, they look like shrubs and in some cases like Bonsai trees with one or two branches that were missed at the previous pruning. This is all done deliberately for very specific reasons. The sacrifice branch is a necessity in Bonsai growing.
Why do we need to do this? The main reason is to enhance growth in a specific area. The theory is that the branch that is allowed to just grow and increase in length will have more sap flowing through it, therefore more nutrients and in turn you get a much faster growth rate compared to regularly pruned branches. One specific case would be to thicken the main trunk. This could be either during the early years after a seed has germinated or a cutting has struck. The more side branches you have that can grow, the thicker the trunk will become. The leader is of importance here. Let this grow until you get to the desired thickness and then cut.
Another reason is to improve taper. If a branch or two are left on the trunk to grow out, the area below the branches will thicken more than the area above it. This leads to a thicker bottom half if the branches were left halfway up the trunk, compared to the top half of the tree.
Another reason for letting a sacrifice branch grow is to get a side branch to thicken in proportion to other branches. An example of this could be that a branch is needed lower down on a trunk and the branches above are all thicker than the lower one. The lower one is then left to grow until the desired thickness is attained and then it is cut back.
There are a few things to keep in mind when sacrifice branches are used. The first one is to remember that the sacrifice branch will create more shade than other branches and this could impact negatively on the growth patterns underneath this branch. A second point to remember is that sacrifice branches that are cut back, can leave quite large scars that will have to heal over time. For trunk thickening it could be best to use a branch at the back or in a place where the design of the tree will hide the scar. A third point to mention is that side branches will start to grow upwards. This growth needs to be controlled if the branch is suppose to be horizontal or even growing slightly downwards.
In the examples below, sacrifice branches were mainly used to thicken side branches to either fill a gap, create a new branch or to correct parallel branches.
Top left: There are two vertical branches parallel to each other growing from the main trunk as well as two bar-branches at the bottom.
Right: the one parallel vertical branch was removed and a new branch allowed to grow out at an angle, removing the parallel effect.
Bottom left: The sacrifice branch and the vertical branch in close up to compare the thickness. This is one season’s growth for this maple.