Final answer:
Volcanic activity has beneficial outcomes including the formation of the Hawaiian Islands, enhancement of soil fertility, and provision of geothermal energy, while sills are associated with magma cooling but are not a direct product of volcanic activity.
Step-by-step explanation:
Beneficial products of volcanic activity include the creation of the Hawaiian Islands, the production of fertile soil, the availability of geothermal energy, and the appearance of geological formations such as sills.
The Hawaiian Islands themselves are an example of this, having been formed from volcanic activity above mantle hot-spots, while geothermal energy is harnessed from heat provided by active volcanoes, as is notably done in Hawaii. Additionally, volcanic eruptions contribute to soil fertility through the dispersion of mineral-rich ash, which enhances agricultural productivity.
Sills, which are formed by the intrusion of magma into parallel rock layers, do not necessarily result from volcanic activity alone, but they are associated with the cooling of magma.