Those rules are fine if you only wear ill fitting suits.
If your suits are cut well, the buttons need to be done up to hold the structure and accentuate the lines of the wearer. In an ill fitting suit, of course, leaving them undone gives the suit more flexibility to move about and mould to the wearer thus hiding the fact that it doesn't fit so well.

The only buttons that should be left undone are the bottom buttons on the cuffs. And even that's discretionary.
(Benjimawoo, Thu 4 Oct 2012, 23:06, 1 reply)

Genuinely interested in your comment
I know on here most comments can come across as defensive or trolling. Must have had close in 50 suits in my time, 4 made to measure (2 on Saville Row (married twice!)). But never heard anything other than the rles above.
( herd of chickens First part only £1.99 and comes with a free, Thu 4 Oct 2012, 23:25, closed)

What like Jimmy Saville suits?
Or perhaps you meant Savile Row.
( @><|= w0nu!) or cunt to my friends, Thu 4 Oct 2012, 23:53, closed)

No, as stated I meant Saville Row
My suits are made from nylon and they only cost a hand job in the back of a Rolls Royce.
( herd of chickens First part only £1.99 and comes with a free, Fri 5 Oct 2012, 0:14, closed)

Ha ha!

( @><|= w0nu!) or cunt to my friends, Sun 7 Oct 2012, 19:50, closed)

It's all about gravity and that
well if you're genuinely interested...

If your suits hangs well you may (/may/ mind) be able to get away with just doing up the top button and the rest of the front will hang with the buttons in line with the holes. This only works on a 2 button suit. It may hang fine, but it looks rubbish in a 3 buttoned suit, and one button... well... it's a bit all or nothing there.

If you leave the top button undone the weight of the coat naturally pulls down and back which causes gaping at the top button, and an unsightly gap at the back of the collar (as the whole coat has shifted back). It also droops down over the shoulders (damn you gravity!) and a) makes your coat look too big because your shoulders don't go all the way out to the top of the sleeves and b) makes the sleeves hang a bit longer than they should, thus covering too much of your shirt cuff.

You might (and again, this is fairly tenuous) be able to get away with it if you're Mr Strong from the Mr Men and have perfectly square shoulders. If your shoulders are perfectly level, then it might not droop down. I haven't' tested this, though, as I don't know Mr Strong.

Oh, and make sure you're the right shape for the number of buttons too. (the photo of Alexei Sale reminded me - Regardless of which buttons he's done up, I bet when he's not doing comedy he wears a 2 buttoned suit, which suits his shape better).
(Benjimawoo, Fri 5 Oct 2012, 20:07, closed)