I will try to not geek out and confuse you on this post. With AutoCAD 2010 there is an AutoCAD 2010 System Requirement to have a CPU (essentially the computer’s brain) with SSE2 support. SSE2 is an Intel CPU instruction set (SIMD Extension 2) which is essentially technology to replace the old MMX extensions which are half as slow in many data and math operations. Most current systems will support SSE2 except an old AMD CPU system over 6 years old. AMD Opteron, Athlon 64 both support SSE2 and have since 2003.
So why SSE2 requirement in AutoCAD 2010:
In developing software there is a limit on how old of technology you can effectively support without impacting current hardware and software users. In the case of AutoCAD 2010 adding the SSE2 requirement this increases performance for customers using current hardware. Many areas improve in AutoCAD such as OSNAPs.
I said I would not geek out so I will not go into details on floats, floating point, and registers. Your experience may vary but the change was made for some performance benefit of current hardware.
Bottom Line: Increasing performance is a good thing!