Visual examination of the voicebox (larynx) carrying the vocal cords, which is located below the back of the throat is called laryngoscopy.

Laryngoscopy is needed due to the following:
Diagnosis of difficulty in swallowing or breathing, longstanding cough, throat or ear pain
Check for inflammation, bleeding, voice problems (breathy, weak, hoarse, or no voice)
Rule out blockage or narrowing of the throat, or remove foreign objects
Check or biopsy a mass or tumour (throat, vocal cords)

You will be advised to avoid eating or drinking water by your doctor for eight hours prior to the procedure, which will be decided on the type of anaesthesia you would be administered. In case you will be administered mild anaesthesia which is generally given you will not be advised to fast.

You should follow specific instructions to prepare yourself for laryngoscopy, which include:
Avoid eating or drinking fluids for eight hours prior to the procedure
Inform your physician about any underlying disease, bleeding problems, past surgeries, or any drugs you take regularly
Discuss risks and other doubts about the procedure
Get all the recommended tests done

Yes, there are infrequent rare side effects of laryngoscopy, which include bleeding, swelling or pain in the throat, mouth and tongue.