Question

Which situations does the combined gas law enable you to do calculations when the other gas laws do not apply?

Answer 1

In most cases you use Boyle's law when Temperature is constant and only Pressure and Volume change;

We use Charles' law when Pressure is constant whereas only Temperature and Volume are changing.

So, what if all three(Pressure, Volume, Temperature) were changing?

That's when you would use the combined gas law!