The idea
Current planning law classifies non-residential properties into a multitude of use classes, and in most cases planning permission is required for change of use from one class to another. Local councils use these use classes as a way of reserving certain properties for uses they consider appropriate, but often without clear links to actual needs or to what the market can bear. Thus many properties remain empty for years because there is no viable use in the class the property has been assigned to, whereas others who want to use the property are not allowed to for no good reason. This has a damaging effect on small businesses and on community groups. For example, in cases I know of personally, a community organisation was refused permission to open a former shop as a cafe (because a neighbouring shop had been given this change of use permission but was in fact still in use as a shop) and in two separate cases (one overturned on appeal, another currently subject to appeal) permission was refused for industrial buildings that had been empty for years to be used by churches. Some restrictions on change of use of premises may still be needed e.g. to control fast food premises, but these might be better handled by licensing authorities rather than planning officials.
Why is it important?
These change of use restrictions are damaging for small businesses in that they do not allow these businesses to use the premises in the locations which are best for the business, or they require slow and expensive bureaucratic procedures to get this permission. They are even more damaging for community groups which need to be at the heart of the community they serve, but are not allowed to be. A side effect of the restrictions is that premises which could be used profitably remain empty, and areas become run down and prone to crime. The restrictions would appear to be a remnant of socialist style central planning of business activity. This kind of central planning clearly does not work and is not a part of the society which the people of the UK now want. Instead user demand and the market should be allowed to determine, with some rather limited restrictions, which kinds of businesses should be allowed to use which premises.