Ok,
Bit bored with no wind about, gives you time to think.
Do people interchange between outside/inside straps only on front or rear?
For example: On a typical 100 litre fsw board, Using the centre strap in the rear, and on the front straps using the furtherest outside position.
Would this comprosmise your stance too much or is it best to keep the fronts straps on the inner position when using the rear in the centre?
I switch to rear centre position (single) when in waves and it tends to make you stand more vertical which is what you want e.g. better for wave riding etc. and set them back outside when I blast in flat water, you can really load up the fin and feel it.
Personally, my board has one strap on the rear & the front straps are out. This is mainly due to me rushing to alter my rear straps a while back when I had a crack at waves. Most of my sailing is chop-hopping, blasting and rarely picking up an odd wave, so it suits ok - but not ideal. I would prefer to have both the front & rear straps out for speed, but when I do get out in waves & it's difficult to not stack on a wave with your feet on the outside rails! I guess I should set the straps each time, but I'm always in a hurry.
As Nosinka said, upright for waves to allow weight distribution for tight turns. As a guess, if you have a wider board with front out & back in, your feet will either be fighting each other if you're attempting wave-riding, or you won't get the best results if going for speed.
works quite well for bumap and jump where you wanna do loads of jumping but are usuing bigger sails say 6.0 and up, i quite enjoy the straps on the outside, and you can still do spocks, forwards tricky tho with a big fin 
