Bioguide sometimes handles like a wet noodle. If it collapses at all into the defect or if your bone graft underneath the membrane puckers in, then you won't get the amount of bone you're looking for. Also, bioguide doesn't stay around very long (about a month or so) and bone takes 4-6 months to heal fully. Nonresorbable membranes (PTFE, titanium mesh) can potentially stay in until you really know that the bone is done healing and a reinforced membrane will keep the space for you. This is especially advantageous for large defects or lateral ridge augmentation. True, it's tougher to find nonresorbable membranes these days (most clinicians shy away and resorbable membranes can handle many things), but they definitely still have their place. Does your school not use them at all?
You seem to have questions that are all-or-nothing. It's great that we have a wide range of materials and procedures to assist our patients. If you're interested (seems like you are), you'll be able to really understand the nuances for each appropriate application once you get to use them. For now, I would see if you can sit in on surgeries that use membranes and maybe you can get a better idea of their indications/properties.
