Photo Source: Summerhill

Taking the time to properly cut and fit the insulation in these areas can impact the effective R-value of the insulation, the condensation resistance of that area, as well as occupant comfort.

(The above photo shows a common way of insulating attic walls. The strapping is a good idea, BUT in this case it is causing compression of the batts and deforming them at the same time. This will lead to increased heat loss at the compressed areas and at the gaps formed.)