I'm not sure whether everyone needs a support group, but it's hard for me to find a downside to having one around.
There's something very comforting for me in being around people who have been where I've been and have wisdom to impart that I may apply to my personal recovery. After all, my best thinking got me to the point whre I needed recovery in the first place. Going it alone, for this person, is clearly not the best idea...
I sometimes think of AA/NA/OA/Triple-A/Frickin' A/Al-Anon/Nar-Anon/and so on-anon as Near-Death Experience Survivors groups. If you're alcoholic/addicted or have lived with the disease of alcoholism/addiction, you've had a near-death experience. Simply put, you've lived near death. It helps to hear others' experience, strength and hope on such subjects.
Books are fine... but books can't hug.