So that you can see if bacteria is present on the specimen and institute empirical therapy before that bacteria is cultured (24-48hrs) and hopefully save the person's life, where in some cases the patient may die before the exact strain of bacteria (and subsequently which antibiotics to prescribe) are known.
Well I would say the value is pretty much disputed..gram staining helps us in identifying whether an organism is gram positive or negative but reveals morphology ie identity of only some species such as staph aureus(Gram +ve cocci),Bacillus anthracis(Gram +ve rods) etc,with this information depending on the condition of the patient you can start empirical bacterial therapy,that is you don't have a definitive diagnosis as to what the organism is but you start treatment any ways to save the life of the patient. Certain antimicrobials are selective for Gram positive while others act more against Gram negative,so based on your report you can start your treatment meanwhile culture sensitivity must always be done as mixed infections are quite common and anaerobic organisms,are not identified by Gram stain alone.
