Wood can be an important part of mothering that can often be underlooked after the initial setup and a good number of wood blocks are created. However wood may be needed later.
Planting involves placing tree saplings so they will grow and be easily harvested without using bonemeal. If done early enough after the setup you may not even need to use all of the bonemeal.
The most important part of planting is that the future tree must have the space to grow and won't get in the way of the drop pool or get burned by the cobble generator.