Sampling Error, Homogenous Mixture, Heterogenous Mixture: Benefits/Drawbacks

[ASidd]

Why do you have to use a homogenous mixture in an experiment what are the disadvantages of using a heterogenous mixture?

 

[mfb]

Mixture of what, in which experiment?

My guess: If you use some specific amount of a heterogenous mixture, the ratio of the components inside (in that specific amount) might differ due to random fluctuations.