matching required for transistors

Hi all i understand the importance if matching and the effects that result due to bad matching. But my doubt is say we take a current mirror. So here the current to be copied is dependent on the factor that all the transistors in the current mirror should be fabricated avoiding any mismatch. So we can see one transistor dependent on the other. But what does dependent mean here??? And why is this important to match only some transistors in the circuit.
Suppose say we have a current mirror matched and say another transistor not belonging to the current mirror is just laid separately. Won't it affect the desired function of the circuit even if the current mirror transistors are matched?? So does every single transistor in the circuit need matching or can some be ignored. If some are ignored (as in kept seperate without any centroid or any other form) so on what basis should we know which transistors to choose for matching and which not. Pls help

Preethi, this has been explained to you again and again: transistors with the same function should be paired, others don't need. If you don't understand this conclusion, you should tell why, then you may get more help.