Life is a chain of strains and stresses intermingled with happiness. It's the same with fabrics. Fabrics undergo a lot of stress during drawing, spinning, weaving, wet processing and mechanical finishing. Since fabrics woven or knitted get physically deformed with all the above processes, they tend to lose their dimensional stability creating severe problems for garments stitched out of such fabrics.
It is therefore imperative to relieve fabrics of any stresses and bring them to a relaxed stage before they are cut and sent for garment manufacturing, or are put to any use.