Mayo Clinic defines acute sinusitis as swelling and inflammation of spaces inside your nose (sinuses). This condition interferes with drainage and causes mucus to build up. 
Mostly caused by common cold, it usually resolves within a week to ten days unless a bacterial infection develops.

Symptoms

Common signs: Thick yellow or greenish mucus from the nose (runny nose) or down the back of the throat ( postnasal drainage). Blocked or stuffy nose (congested) causing difficulty breathing from your nose 

Pain, tenderness, swelling and pressure around your eyes, cheeks, nose or forehead that worsens when bending over.

Other signs and symptoms:Ear pressure, Headache, Cough, Fever 
Other benefits 

Nasal saline irrigation may reduce the need for pain medication and improve overall patient comfort, particularly with patients with frequent sinus infections.
Studies have shown that nasal irrigation with isotonic and hypertonic solutions provide benefits for symptom relief.
Research suggests that intranasal saline spray may temporarily improve nasal passage patency by moisturizing and loosening secretion. This approach may be useful in combination with intranasal steroids.

Reference:
E. Santoro et al. The role of saline nasal sprays or drops in nasal hygiene: a review of the evidence and clinical perspectives.  Rhinology online, Vol.4: 1-16,2021. D. King et al. Saline nasal irrigation for acute upper respiratory tract infection.  Cochrane Database Syst Rev (2015)