> Microinstructions formats take advantage of the fact that, at the microprogramming level, many operations can be performed in parallel. If all useful combinations of parallel microoperations were specified by a single opcode, the number of opcodes would, in most cases, be enormous. Furthermore, an opcode decoder of considerable complexity would be needed. To avoid these difficulties, it is usual to divide the microoperation specification part of a microinstruction into k disjoint control fields.
> Each control field handles a limited set of microoperations, and one of which can be performed simultaneously with the microoperations specified by the remaining control fields. A control field often specifies the control-line values for a single device such as an adder, a register, or a bus.
I do not understand how does controol field division into k disjoint fields helps?