There are many different attributes which can be defined as part of a style. However, they do not all have to be defined in each style, and there are advantages to defining fewer rather than more attributes for each style.
If you define only some attributes for each style, you can apply more than one style to the same text. For example, you might want a currency style, with the number format including a £ sign, and a Totals style, which highlighted the contents of the cell in bold. Defining these as separate styles would give you increased flexibility; rather than having to create a separate style for each combination of attributes, you can simple apply several styles to the same cell.
Non-text style attributes, such as number and date formats, background colours and table grid information, should always be defined separately from text styles. This gives you a great deal more flexibility in changing the design without affecting the text it contains.