It's an optional component of spybot.  It prevents things like your home 
page being changed with out your consent.  It's a good thing most of the 
time.  It also pops up warnings if anything wants to change a regestry 
setting.  As I say usually a good thing to.  I haven't however had spybot 
find anything since I installed windows deffender, so I am thinking that 
both are not necessary.  Your choice.