glycogen breakdownw serves different purpose: to releas glucose into blood when glucose blood drops, as it does betwen meals. it requires an enzyme, glucose 6 phosphatase, an integral membrane protein which is predicted to contain nine membrane helice, its active site located in lumenal of endoplasmic reticulum. This enzyme is present only in kidney and liver, not in other tissues. the glucose 6 phosphate is formed in cytosol and transformed into ER by specific transporter (T1), hydrolized by glucose 6 phosphatase in surface of lumen. the resulting of PI and glucose are though to be carried back to cytosol via two different transporters (T2 and T3). The glucose leaves hepatocytes via yet another transporter in the plasma cell, GLUT2.
notice by having the site active of glucose 6 phosphatase in the endoplasmic reticulum lumen, cell seperates glucogen breakdown and glycolisis which happens in cytosol and would be aborted by the action of glucose 6 phosphatase.