Naming the causative organism changes antibiotic choice, isolation precautions, and prognosis. Each of these is a clinical decision, not a laboratory curiosity.
Empiric therapy is a guess with a deadline
Empiric therapy (treatment started before the organism is known) is chosen from the likely pathogens for the infection site, the patient's history, and local resistance patterns. It is deliberately broad because being wrong early is dangerous. Identification exists to end that guesswork: the same patient can be switched to a narrower agent that matches the actual organism, which lowers collateral damage to the patient's own flora and slows the emergence of resistant strains.
Two patients, same Gram stain, different rooms
Two patients both have a Gram-positive coccus growing from blood cultures. If the organism is identified as Staphylococcus aureus, contact precautions and screening for carriage become relevant because this organism spreads readily between patients. If it is identified as a coagulase-negative staphylococcus, the same Gram stain finding usually points to skin contamination of the blood culture rather than a bloodstream infection, and no isolation is triggered. The Gram stain alone could not separate these two paths; the species-level identification did.
Identification also sets expectations
Some organisms carry a predictable clinical course and complication risk. Knowing the species lets the team anticipate complications, decide how long to treat, and judge whether the patient is responding as expected. An unidentified organism leaves all of this open.