Why use a cutting fluid?
No matter how good a fissure is when scored dry, it is better if scored with a liquid between the wheel and the glass. Several good things happen with an "oil" cut and only one undesirable thing.
The bad thing is you have to wash the glass afterwards, but in many cases washing is required anyway.
A good thing is the fluid reduces the effect of healing - the compressive strength overcoming the fracture caused by scoring. It is probable that the liquid seeps into the fissure contaminating it enough to prevent atomic reattachment of the molecules.
Cutting oil reduces chipping and prevents a flaky score line. The oil tends to provide a hydraulic cushion between the glass and the wheel. This allows more uniform transmission of the shearing forces into the glass at an angle dictated by the wheel, not by particles of crushed glass.
It is important to check the cutter wheel is moving freely, since a wheel not rolling freely may skid. Skidding causes abnormal wear to the wheel and subsequently it becomes a skipper.
You should not use kerosene by itself because it removes whatever oil is on the axle.
Prepared from information provided by Fletcher-Terry company