There is no one size fits all cutting fluid, though many fluids can be used for many different operations it doesn't make them optimal for those operations. The purpose of the cutting fluid is to reduce heat. Some do it by reducing friction (oils), others do it by convection and reducing friction to various degrees (soluable oils, semi and full synthetic coolants).
Drilling in particular is a challenging operation to lubricate or cool properly that people take for granted. The (typical HSS twist) drill is doing two things, at the center web where the surface speed is near zero, it's extruding the material. At the cutting edge where the flute meets the face, it's cutting material. The heat is generated by the friction of the extrusion, as well as by the friction of the cutting action, and to a lesser degree by the lands of the drill rubbing on the drilled hole wall, and the chips traveling up the flute or becoming compacted in the flute and then rubbing on the drilled hole wall.
In order to cut, you want an oil that lubricates the surfaces of the work and tool that are rubbing but not the actual cutting edge. The entire operation is dependent on the cutting edge biting into the work, which requires some amount of friction. This is why oils that are meant for reducing wear on parts meant to slide across each other such as ATF or motor oil are poor cutting fluids. Their long polymer chains have tight bonds that are designed not to break under extreme pressure (like the cutting edge of a tool or the piston ring in your car). It's also why animal fat does in some cases work well, the bonds are not as strong and break under that high pressure while remaining intact under lesser pressures (such as chip/flute contact.) Sulphurized, chlorinated, or molybdenum types of cutting fluids also work on this principle of providing the right amount of lubrication for the right amount of pressure and breaking down where the cutting occurs.
Then there's the workpiece component. WD40 or kerosene or any light mineral oil works well with Aluminum because the extrusion of the material is relatively easy, the cutting is relatively easy, and you're not trying to avoid the kind of heat that breaks down the cutting edge, rather the kind of heat that allows the material to solder to the cutting tool. Lubrication is less important than convection, which light oils do better than heavy oils, while retaining some small amount of lubricity in comparison to say water. Higher demands require higher lubricity.
Tapping titanium is maybe one of the more demanding operations a knifemaker will do. Taps have a lot of surface area contact. They are small diameter in relation to the amount of cutting force required. They have very little or no relief behind the cutting edges. Titanium deflects and has a lot of spring back, resulting in what amounts to something like a chinese finger cuff around your tap. This is why high lubricity high pressure cutting fluids like Moly Dee are preferred for operations like this.
If I was going to have one cutting fluid in my shop to handle everything, it would be regular sulfurized pipe threading oil. For drilling, tapping, reaming, and milling with HSS endmills or slitting saws. It will work relatively well in just about any HSS tool/steel work situation.
I prefer to have Moly Dee or Boe Lube or at least Tap Magic for tapping titanium and stainless or high alloy steels. Kerosene for Aluminum unless tapping deep holes, then an aluminum tapping fluid is handy. And a synthetic coolant for misting HSS endmills or flooding surface grinders.
