Boss VF-1 Effect Processor

I believe that when using a guitar amp with this "little red Boss box"
the best thing to do is run the vf1 into the effects loop if
available. Is this true? If it is , then how should I do this on my
guitar amp.....Loop "send" or "return" in; or in series in the loop?
Also, then should the vf1 be set to "Line" or one of the "Guitar
combo" or "Power amp stack" settings?
Obviously if no guitar amp is used but I go straight into a PA; the
vf1 should be set to "Line", right?
Are you guys going to just tell me to try all the settings and pick my
favourite?
I don't quite get the manual. I just want to know what the best option
for a VF1 is with maybe: a Laney VC30 combo, or a JCM 800 head & quad,
or with a Fender twin? 
Too many questions?...Sorry. Any ideas appreciated. Thanks.

Jon