You can plant an aloe vera outside if you live in USDA Hardiness Zones 10-11, which includes areas of Florida, California and Hawaii.
Aloes make great container plants. If your aloe vera is in a container and you do not live in zones 10-11, allowing your plant to spend the summer outside is beneficial.
Aloe vera is a medicinal plant. Its gel soothes sunburns and moisturizes dry skin, and aloe capsules may sooth upset stomachs.
There are over 250 species of aloe, including aloe vera. While aloe vera is not the only medicinal aloe, it's certainly the best known.
If you plant your aloe outside, choose a full sun location and use a mix of well-draining soil and sand or a cactus potting soil. As with all succulents, water the plant infrequently.