When should blade coolant be used?

Like the name suggests, a coolant (whether a spray or dip), will cool your blade, and depending on the brand, may clean and disinfect also. Use blade coolant when your blade is getting hot. Check your blade while in use. Touch the blade about every 10 minutes (this depends on the speed of your clippers and how hard your blade is having to work).

A hot blade risks burning the animal, and causes a blade to become dull and blunt faster than normal. Spray on coolant, or dip your blade in coolant, to quickly cool it. Run it for a few seconds. Apply 2 to 3 drops of oil and continue clipping. 

A coolant may lightly lubricate but does not replace the need for oil. Coolants will often clean the blade also, including removing oil, so it's normal to need to reapply a little oil after coolant use to keep blades lubricated. Oil helps keep blades cooler by reducing friction, but oil does not replace the role of coolant.

Some coolants also clean and sanitise. Use multi-purpose coolants to clear out fur built-up between teeth and clean blades after use, to sanitise between clients, and when moving from sanitary areas like the rectum, to the face.