IE9中的IE7/8模式与实际运行的IE7/8相比有多好

I'm trying to confirm this for work purposes so we don't need to have separate VMs to test in IE7 and IE8. I've always just used the developer tools in IE9 (F12) and changed the browser mode and document mode to do IE7 and IE8 testing.I'm trying to confirm this for work purposes so