What are Elizabethan collars?
Traditional Elizabethan collars ("E-Collars") are common hard plastic devices applied around the neck of pets. In some instances these collars are also known as cone collars, protective collars, recovery collars or recovery cones.

Benefits of Elizabethan collars
Elizabethan collars are especially useful in post-operative situations to avoid self-trauma at the surgical site, and to allow optimal healing to occur. Many veterinarians will routinely use these collars in all soft tissue and orthopedic surgeries done in pets, especially when sutures and/or staples are used to close the skin. Protective collars also come in handy to avoid self-trauma associated with hot spot allergic dermatitis, as well as to prevent unwanted chewing of skin growths or tumors.
Typically, e-collars are left on for 7-10 days post-operatively and for a similar period when allowing for maximal healing of allergic hot spot dermatitis. Although there are BiteNot collars that may be useful as alternatives to Elizabethan collars, I have found these to not be as effective as traditional Elizabethan collars.