I was not refering to a specific definition but would suggest that a Parish Council with, say, allotments, cemetery, playing field etc would be best splitting their costs into cost centres. If the Parish Council was just responsible for a bus shelter and playground, for example, cost centres are less important as the spend would be easily identified.
There is a definite legal requirement for parish councils with income or expenditure of over £200,000 to publish their spending with cost centres defined. This is detailed in the Transparency Code for Larger Authorities.