tube amps ... pedals

Hi there

Got a question about tube amps vs pedals.

I started of on a Hot Rod Deville 212 with a Triple Wreck but I didn't like the humming sounds etc etc and I always heard tube amps with distortion were better etc. So I bought myself an Engl Gigmaster 15 head with a n Engl 2x12 pro cab (vertical).

Now after a lot of searching and confusion ... what's the actual difference between a distortion pedal and an amp that gets distorted by the tubes.. to me it sounds better but, then why do people use pedals for distortion? Some use boost + OD to get distortion, others just boost... or others even use OD or Distortion pedals on there lead channels? I'm confused, why would you use a pedal on a lead channel?

I'd love to have a bit more gain/heavyness on my Gigmaster so I figured out I just need a boost to push the preamp harder and get more gain right? But why do some people OD for that matter?

I also like to have a fuzz sound, so I've only seen pedals who make the fuzzy sound. Or are there amps out there who can make a fuzz sound by their own or is there a way possible to make your amp do this?

Last... isn't a pedal just an emulation of what tubes can do? It feels "wrong" to use a pedal as it won't be as good as a tube amp sound right? What's the big advantage of all the pedals, I see lots of people using them ON their tube amps but I don't know why...

Thanks

Jesse