There is no real evidence that aloe vera (Aloe barbadenis) helps the skin in any significant way, though it's not a throwaway ingredient. Some brands use aloe in place of water in their products, but aloe is actually 99.5% water (Sources: Indian Journal of Dermatology, volume 53, issue 4, 2008, pages 163–166; and http://apps.who.int/medicinedocs/en/d/Js2200e/6.html#Js2200e.6).
There is research indicating that isolated components of aloe vera, such as glycoprotein, can have some effectiveness for wound healing and as an anti-irritant (Sources: Journal of Ethnopharmacology, December 1999, pages 3–37; Free-Radical Biology and Medicine, January 2000, pages 261–265; and British Journal of Dermatology, October 2001, pages 535–545). However, when mixed into a cosmetic product, it is doubtful those qualities remain, although it may still play a role in binding moisture to skin (Source: Skin Research and Technology, November 2006, pages 241–246).
In pure form, aloe vera’s benefits on skin are probably its lack of occlusion and the refreshing sensation it provides. Aloe serves as a water-binding agent for skin due to its polysaccharide (complex carbohydrate) and sterol content. (An example of a sterol that’s beneficial for skin is cholesterol) Although research has shown aloe also has anti-inflammatory, antioxidant, and antibacterial qualities, no study has proven it to be superior to other ingredients with similar properties, including vitamin C, green tea, pomegranate, and many other antioxidants (Source: www.naturaldatabase.com).