In most cases the trim can be left on and we can sand up to it without any trouble. A few exceptions to this however, are when we are using a pigmented stain, because it will transfer to the trim. This can also affect door casings which we do not remove. Another reason we may recommend removal is if the trim is eventually being replaced. If the trim profile changes after we’ve sanded, it leaves the un-sanded lumber exposed in the future. Lastly, if a trim is so custom, delicate, unrepairable, or irreplaceable, we may require that the trim is off when we sand. This may hold true for unique paint colors that cannot be touched up. We generally don’t work with trim that is so unique and we will generally require clients to have their carpenter remove and replace it, or plan to repaint. If the trim falls under this unique category let us know and we can address that beforehand. We have more information on sensitive trim here.