The most important physical property of platelets is the maintenance of Hemostasis, and it depends on three factors
The endothelial supporting function of platelets,
The ability to form hemostatic plugs and
To release lipoprotein material (platelet factor 3).
When these circulating platelets get reduced, the capillary endothelium gets weak, because the platelets are not available to enter the endothelial cytoplasm for the support. And hence, the capillary walls gets ruptured when expose to trauma. The bleeding through the damaged capillary walls is arrested by the aggregation of the platelet making a hemostatic plug. This is the main function of the platelet or the most important physical property of the platelet.