What's the advantage of having nonvolatile registers in a calling convention?

Question

I\'m programming a JIT compiler and I\'ve been surprised to discover that so many of the x86-64 registers are nonvolatile (callee-preserved) in the Win64 calling convention.

Answer 1

The advantage of having nonvolatile registers is: performance.

The less data is moved, the more efficient a CPU is.

The more volatile registers, the more energy does the CPU need.