I work for Cyril Flint.org as a weekly volunteer. You're matched up with a suitable client, and are mentored by the volunteer organiser until she's satisfied that you can go solo. This subject to a CRB check. The man I visit is called Paul, who is an intelligent, articulate, knowledgeable, and likeable bloke. He recently suffered a severe stroke, and as a result is housebound most of the time, until the weekend, when a family member takes him out.
I believe that what Paul gets out of the visit is a chance to talk with somebody who's not a medical carer or a member of his family. What I get out of it is the chance to meet somebody different, and hopefully make some small difference to his daily routine. We've different views on some subjects, which makes for some interesting conversations at times, which we both really enjoy.