An internal progress clock allows you to intuitively understand how far you’ve progressed in a GRE quant question. Are you close to getting a correct answer? Halfway? A third of the way? Knowing your approximate progress in solving a quant problem can help you determine whether you should keep working or make the best possible guess and move on to the next question.

Much of this comes down to being familiar enough with the various GRE quant question types to know, in general, the steps that it will take to solve a particular question. This is yet another reason why ample, methodical practice with realistic GRE questions is essential to your GRE prep.