Blood is powerful.

Blood (or its equivalent in beings without it) carries essential substances through a body, whether they be oxygen, nutrients, or other. It removes waste. It is both nurturing and cleansing. Blood is also damning. Stained on hands, it declares guilt. It carries dark powers as well as holy. Because blood is part of the body, it has nommos inherently in it.

On a supernatural plane, blood is also responsible for carrying certain supernatural properties. Notably, it is the main method of moving qi (lifeforce, ashar) through the body. It can also carry msawhat, aether, infernum, heghn, mana, void, poioumenon, emotion, dumaqu, radiance, arnum, flux, yahas, draconic power, Damaskian power, and more. Therefore, one who uses blood has access to multiple forms of energy.

Historically, bloodcasting was accessing mana through the blood, but since Starfall, this has expanded greatlty. Hematophagy is another form of blood-empowerment that is extremely common.

Blood is a common ingredient in ceremonies of all types, religious, magical, and so on. The blood of a powerful being is incredibly potent.

So here's how blood can be used:

Hematophagy - gaining power through drinking blood
Bloodcasting - using spilled blood to access mana
Bloodbonding - mixing blood with another to create a supernatural bond (either via yahas or mana)
Bloodsharing - giving blood to another to cause a supernatural reaction (usually heghnic healing, radiant empowering, mswhat or arnic poisoning)
Blood Ritual - using blood in religious, heghnic, or infernal ceremonies
Bloodsplicing - using superscience to alter one's own blood for various powers
Hematurgy - using blood to access shebvic powers (draconic or Damaskian)
Bloodburning - combining blood with emotion to create energy
Redlining - drawing with blood to create binding contracts or effects
Bloodmisting - intentionally altering one's own blood pressure such that tapping into one's blood stream creates a spray of blood, which then creates a powerful effect

Other powers are possible.