It is forbidden to smell the myrtle 1. It is forbidden to smell the myrtle that is used for the mitzvah. Technically, it is permitted to smell the etrog, but because there is a disagreement about whether or not to bless on it, one should refrain from smelling it.
2. If [one of the four species] was made for [use as one of the four species] but was not lifted to fulfill an obligation, it is still permissible to get benefit from it [by using it for a non-mitzvah purpose].