I ran into this video which gives a nice insight in why some believe the Google Sandbox is bad for business:

But what is it really? Google’s definition is:

"A filter affect that Google places on new domains to stop the website from high rankings for the main keywords."

Wikipedia says:

"The Sandbox (a.k.a. Sandboxing or the sandbox effect or the Google penalty) is a name given to an observation about the way Google ranks web pages in its index. It is the subject of much debate—its existence has been written about[1][2] but not confirmed and several observers state that they have observed the contrary"