Why would doctors typically want to do a bronchoscopy?

Diagnosis/Therapy. Bronchoscopy is one of the main procedures performed by pulmonologists to help in the diagnosis of lung disease. Inspection of the airways is performed. Sometimes fluid or tissue is obtained for further analysis. Bronchoscopy can also be used for treatment of lung cancer, narrowing of the airways, and other lung problems.
Many reasons. To evaluate the anatomy of the bronchioles. Other reasons include rule out infections, evaluate masses and in some cases, sample enlarged lymph nodes. Sometimes, we biopsy bronchiole wall to evaluate for immune disorders.
Depends. On why it's done. If it's to clean out a mucous plug, then usually just suctioning. If it's done to look for infection, then maybe a bronchioalveolar lavage (BAL) and potentially biopsy. If its done looking for cancer, then biopsies and BAL. Brushes are also commonly done to get the lung tissue cells to be looked at for cancer. Ultrasound can also be done.
Better view. To getter a direct view of your upper and lower airway. They get also a chance to get some liquid for cultures and possibly, if indicated, a biopsy.