If beyond this limit then Squid forwards the Range request as it is and the result is NOT cached.
This is to stop a far ahead range request (lets say start at 17MB) from making Squid fetch the whole object up to that point before sending anything to the client.
A value of -1 causes Squid to always fetch the object from the beginning so that it may cache the result. (2.0 style)
A value of 0 causes Squid to never fetch more than the client requested. (default)