The sutures of the skull have several important roles. In development they are straight edged and lie on top of a network of soft cartilage and connective tissue to allow the head of the newborn to deform in order to fit through the narrow birth canal.
In adult life the main function of sutures is to distribute impact force evenly around the skull. The collagen present in the interfacial layer coupled with the jagged interlocking distribute impact force evenly across the entire length of the sutures and connecting bone. They are around 5 times stronger under impact than pure bone and as the collagen content goes up with increased interdigitation they can be stronger.
Under slow compression only extremely interdigitated suture can match the strength of pure cranial bone.
Sources:
HUBBARD, R. P. 1971. FLEXURE OF LAYERED CRANIAL BONE. Journal of Biomechanics,4, 251-&.
HUBBARD, R. P., MELVIN, J. W. & BARODAWA.IT 1971. FLEXURE OF CRANIAL SUTURES. Journal of Biomechanics, 4,491-&.
JASLOW, C. R. 1990. MECHANICAL-PROPERTIES OF CRANIAL SUTURES. Journal of Biomechanics,23, 313-321.
SADLER, T. W. 2010. Systems-Based Embryology. In: HORVARTH, K. (ed.) Langman's Medical Embryology. 11 ed. Philadelphia: Lippincott Williams & Wilkins.
SCHOENWOLF, G. C., BLEYL, S. B., BRAUER, P. R. & FRANCIS-WEST, P. H. 2009. Origin of Skull. In: CRATER, P. (ed.) Larsen's Human Embryology. 5th ed. Philadelphia: Curchill Livingstone.