It will give the people that put rootkits or other what not in the cracked version your bank and other passwords. So in general I tell people to avoid them.
Sheesh isn't it bad enough to have Microsoft and the NSA spying on you? And you'd want to let random crooks spy on you too?
Truth is, there is no reason to pirate Windows 10 because if you never activate it nothing happens except you can't change the desktop wallpaper away from a friendly reminder to activate. That's right, nothing else is broken and everything works just like an activated copy. So by definition, Windows is now the nagware variant of shareware.