being constituted can help in a variety of ways. It gives the organisation a management tool – objectives, furtherance powers, how to operate / make decisions, appoint trustees / committee members are all outlined in the constitution. Some constitutions are more simple / straight forward than others, it really depends on the type of legal structure you want to go for. There’s a variety of templates available – Community Matters provide model governing documents for Community Associations which includes the Charitable Incorporated Organisation (CIO), Charitable Company, Charitable Unincorporated Association and a basic constitution for small groups). Other national bodies like the Parent Teachers Association and Pre School Learning Alliance produce their own model constitutions. The Charity Commission provide generic model governing documents for unincorporated associations, Trusts, Charitable Companies and the new CIO structure.
In my experience, the main driver for most groups who become formally constituted is that grant givers / funding bodies will only consider constituted groups as part of their basic eligibility criteria. I also think being constituted promotes and increases external confidence (e.g. the Local Authority) in the integrity and sustainability of the organisation.