A You certainly won't find anything in the law saying you have to have committees. Governing bodies of county and voluntary schools decide themselves how they want to organise their work, with one exception - which is that you must have a committee to deal with anything that could later lead to an appeal (eg, teachers' pay, discipline, grievance or an exclusion). This is to keep enough governors without previous knowledge to serve on an appeal committee.
I think if they are well run, committees make the work much more manageable. They also give more people a chance to contribute and they increase the governing body's knowledge of the detail of issues. But, of course, if they double the work instead of halving it, there's a heavy price to pay for a bit more participation.
Only have a committee where you can see a real need, and a continuing one. If it's a job you can see the end of, a working party is better. Make sure that the governing body explains its remit carefully, and that people don't try to have the same discussion all over again on the full governing body.
One good way to avoid this is to have open committees to which any other governors can just turn up as visitors. Then if anybody wants to re-run the same discussion they can be pleasantly told that governors interested in the detail should go to the committee. Of course you have full members who are voted on to the committee and only these vote, but it does increase the attendance and the participation if other governors turn up from time to time.