Using EMMS is like emptying a container to accommodate new content. The EMMS instruction clears the MMX™ registers and sets the value of the floating-point tag word to empty.
You should clear the MMX™ registers before issuing a floating-point instruction because floating-point convention specifies that the floating-point stack be cleared after use. Insert the EMMS instruction at the end of all MMX™ code segments to avoid a floating-point overflow exception.
Why You Need EMMS to Reset After an MMX™ Instruction
Failure to empty the multimedia state after using an MMX™ technology instruction and before using a floating-point instruction can result in unexpected execution or poor performance.