Request the ability to apply the format returned by a formula.  This is in essence like the STYLE() function, except applied via conditional formatting rather than by explicit use of STYLE().

Use case: applying a style to manually entered data.  For example, a formula that returns a named style based on the year of an entered date (perhaps by means of LOOKUP()) would have the style applied by conditional formatting to the entered cell.

The date method of conditional formatting is not appropriate for this case; the basic conditional formatting could be used, but only up to 10 years (or other ranges).  It's also less flexible, because the formula to be used for the computed conditional format could actually be a name; editing the value of the name changes the formula, which would allow the computed style to be changed easily everywhere.